Previous Page 152

Purification of Organic Chemicals

P-Citronellol (3,7-dimethyloctan-6-ol) [ R - ( + ) : I 1 171-61-91 [S-(-): 106-22-91 M 156.3, b 4 7O/lmm, 102-104(110°)O/lOmm, 112-113O/12mm, 221-224O/atm, 225-226O/atm, d i 4 0.8551, n i 4 1.4562, [a]:& f 6 . 3 O , [a]iof5.40 (neat). Purified by distn through a cannon packed (Ni) column and the main cut collected at 84O/14mrn and redistd. Also purified via the benzoate. [IR:Eschenazi JOC 26 3072 1961;Bull Soc Chim France 505 19511. S-Citrulline (2-amino-5-ureidopentanoicacid) [2436-90-01 M 175.2, m 222O, [a]io+24.2O (in 5M HCl). Likely impurities are arginine, and ornithine. Crystd from water by adding 5 volumes of EtOH. Also crystd from water by addn of MeOH. p-Cocaine [50-36-21 M 303.4, m 98O, [a]Lo -15.8O (CHCI3). Crystd from EtOH. Cocarboxylase see entry in Chapter 5. Cofazimine [2030-63-91 M 473.5. Recrystd from acetone. Codeine [76-57-31 M 299.4, m 154-156O, [a]: EtOH. Dried at 800.

- 1 3 8 O (in EtOH). Crystd from water or aqueous

Coenzyme Q o (2,3-Dimethoxy-5-methyl-1,4-benzoquinone, 3,4-dimethoxy-2,5-toluquinone, fumigatin methyl ether) see entry in Chapter 5. Colchicine, Colchicoside see entries in Chapter 5. 2,4,6-Collidine see 2,4,6-trimethylpyridine. Coniferyl alcohol [4-hydroxy-3-methoxy-cinnamyl alcohol, 3-(4-hydroxy-3methoxyphenyl)-2-propen-l-ol] [458-35-51 M 180.2, m 73-75O, 73-75O, b 163-165°/3mm. It is soluble in EtOH and insoluble in H20. It can be recrystd from EtOH and distd in a vacuum. It polymerises in dilute acid. The benzoyl derivative has m 95-96O (from pet ether), and the tosylate has m 6 6 O . [derivatives: Freudenberg and Achtzehn B 88 10 1955; UV: Herzog and Hillmer B 64 1288 19311. Conessine [546-06-51 M 356.6, m 125O [a];' from acetone. Congo Red [573-58-01 M 696.7,

A,,

-1.9O (in CHCIs), +25.3O (in EtOH).

Crystd

497nm. Crystd from aq EtOH (1:3). Dried in air.

Coproporphyrin I see entry in Chapter 5. Coprostane (5a-cholestane) [481-20-01 M 372.7, m 72O, EtOH. 4,5-Coprosten-3-01 MeOWethyl ether.

[aID+2S0 (c 1, CHCI3). Crystd from

(cholest-4-ene-3R-01) [ S l 7 - 10-21 M 386.7, m 132O.

Coprosterol (5a-cholestan-3R-01, dihydrocholesterol) 140°, + 2 4 O (c 1, CHCl3). Crystd from MeOH. Coronene [191-07-1] M 300.4, m 438-440°, A,, toluene, then sublimed in vacuum.

Crystd from

[80-97-71 M 388.7, m l o l o , 139-

345x1111 (log e 4.07).

Crystd from benzene or

Cortisol, corticosterone, cortisone and cortisone-21-acetate see entries in Chapter 5. Coumalic acid [500-05-0] M 140.1, m 205-210°(dec). Crystd from MeOH.

Purification of Organic Chemicals

153

Coumaran see 2,3-dihydrobenzofuran. 4-Coumaric acid see p-hydroxycinnamic acid. Coumarilic acid see 2-benzofurancarboxylic acid. Coumarin [91-64-51 M 146.2, m 68-69O, b 298O. Crystd from ethanol or water and sublimed in vucuo at 43O [Srinivasan and deLevie JPC 91 2904 19871. Coumarin-3-carboxylic acid [531-81-71 M 190.2, m 188O(dec). Crystd from water. Coumarone see benzofuran. Creatine (H20) and creatinine see entries in Chapter 5 . o-Cresol [95-48-71 M 108.1, m 30.9O, b 191°, n41 1.53610, n 46 1.53362. Can be freed from mand p-isomers by repeated fractional distn, Crystd from benzene by addition of pet ether. Fractional crystd by partial freezing of its melt. m-Cresol 1108-39-41 M 108.1, f.p. 12.0°, b 202.7O, d 1.034, n 1.5438. Separation of the m and p-cresols requires chemical methods, such as conversion to their sulphonates [Briichner A C 75 289 19281. An equal volume of H2S04 is added to m-cresol, stirred with a glass rod until s o h is complete. Heat for 3h at 103-105O. Dilute carefully with 1-1.5 vols of water, heat to boiling point and steam distil until all unsulphonated cresol has been removed. Cool and extract residue with ether. Evaporate the s o h until the boiling point reaches 134O and steam distil off the m-cresol. Another purification involves distn, fractional crystn from the melt, then redistn. Freed from p-cresol by soln in glacial acetic acid and bromination by about half of an equivalent amount of bromine in glacial acetic acid. The acetic acid was distd off, then fractional distn of the residue under vac gave bromocresols from which 4-bromo-m-cresol was obtained by crystn from hexane. Addn of the bromocresol in glacial acetic acid slowly to a reaction mixture of HI and red phosphorus or (more smoothly) of HI and hypophosphorus acid, in glacial acetic acid, at reflux, removed the bromine. After an hour, the soln was distd at atmospheric pressure until layers were formed. Then it was cooled and diluted with water. The cresol was extracted with ether, washed with water, NaHCO3 s o h and again with water, dried with a little CaC12 and distd [Baltzly, Ide and Phillips JACS 77 2522 19551. p-Cresol [106-44-51 M 108.1, m 34.8O, b 201.9O, n41 1.53115, n46 1.52870. Can be separated from m-cresol by fractional crystn of its melt. Purified by distn, by pptn from benzene s o h with pet ether, and via its benzoate, as for phenol. Dried under vacuum over P2O5. Has also been crystd from pet ether (b 40-600) and by conversion to sodium p-cresoxyacetate which, after crystn from water was decomposed by heating with HCl in an autoclave [Savard Ann Chim (Paris) 11 287 19291. o-Cresol Red [1733-12-61 M 382.4, m 290°(dec). Crystd from glacial acetic acid. Air dried. Dissolved in aqueous 5% NaHC03 soln and ppted from hot soln by dropwise addition of aqueous HCI. Repeated until extinction coefficients did not increase. o-Cresotic acid (methylsalicylic acid) 183-40-91 M 152.2, m 163-164O, m-Cresotic acid [SO-85-11 M 152.2, m 177O, p-Cresotic acid [89-56-51 M 152.2, m 151O. Crystd from water.

&\rm

Crocetin diethyl ester [5056-14-41 M 384.5, m 218-219O, 2340 (400nm), 3820 (422nm), 3850 (450nm) in pet ether. Purified by chromatography on a column of silica gel G . Crystd from benzene. Stored in the dark, under an inert atmosphere, at Oo. Crotonaldehyde [127-73-91 M 70.1, b 104-105O. Fractionally distd under N2, through a short Vigreux column. Stored in sealed ampoules.

154

Purification of Organic Chemicals

trans-Crotonic acid [3724-65-01 M 86.1, m 72-72.5O. Distd under reduced pressure. Crystd from pet ether (b 60-80°) or water, or by partial freezing of the melt.

E - and 2-Crotonitrile (mixture)

[4786-20-31 M 67.1, b 120-121°, d 1.091, n 1.4595. Separated by preparative GLC on a column using 5% FFAP on Chromosorb G. [Lewis et al. JACS 108 28 18 19861.

y-Crotonolactone [ 4 9 7 - 2 3 - 4 1 M 84.1, m 3-4O, 76-77O/3.5mm, 90.5-91°/1 1.5mm, 9293O/14mrn, 107-109°/24mm, 212-214°/760mm, d i 0 1.197, nko 1.470. Fractionally distd under reduced pressure. IR: (CCl4) 1784 and 1742 cm-l, UV no max above 205nm (E 1160 cm-l M-I) and 6 (CC13) 2.15 (pair of triplets lH), 3.85 (pair of triplets 1H) and 5.03 (triplet 2H) 7. [Org Synfh Coll Vol V 255 1973; Smith and Jones Canad J Chem 37 2007,2092 19591. Crotyl bromide [29576-14-51 M 135.0, b 103-105°/740mm, n25 1.4792. CaCO3 mixture. Fractionally distd through an all-glass Todd column.

Dried with MgS04,

15-Crown-5 [ 3 3 1 0 0 - 2 7 - 5 1 M 220.3, b 93-96O/O.lmm, d 1.113, n 1.465. molecular sieves.

Dried over 3A

18-Crown-6 [17455-13-91 M 264.3, m 37-39O. Recrystd from acetonitrile and vacuum dried. Purified by pptn of 18-crown-6hitromethane 1:2 complex with Et2O/nitromethane (10: 1 mixture). The complex is decomposed in vacuum and distilled under reduced pressure. Also recrystd from acetonitrile and vacuum dried. Cryptopine [482-74-15] M 369.4, m 220-221O. Crystd from benzene.

&;rm

Cryptoxanthin [472-70-81 M 552.9, 2370 (452nm), 2080 (480nm) in pet ether. Purified by chromatography on MgO, CaCO3 or deactivated alumina, using EtOH or ethyl ether to develop the column. Crystd from CHC13EtOH. Stored in the dark, under inert atmosphere, at -2OO. Crystal Violet Chloride (Gentian violet, N-4[bis[4-(dimethylamino)phenyl)methylene)-2,5cyclohexadien-1-ylidene)-N-methylmethaniniumchloride) [548-62-91 M 408.0. Crystd from water (20mVg), the crystals being separated from the chilled soln by centrifugation, then washed with chilled EtOH (sol l g in 10 ml of hot EtOH) and ethyl ether and dried under vac. It is sol in CHC13 but insol in Et20. The carbinol was ppted from an aqueous s o h of the HCI dye, using excess NaOH, then dissolved in HCl and recrystd from water as the chloride [W and kinetics: Turgeon and La Mer JACS 74 5988 19521. The carbinol base has m 1 9 5 O (needles from EtOH). The diphthalute (blue and turns red in H20) crystallises from H20, m 153-154O (dec 185-187°)[Chamberlain and Dull JACS 50 3089 19281. C u m e n e [ 9 8 - 8 2 - 8 1 M 120.2, b 69-70°/41mm, 152.4°/760mm, d 0.864, n 1.49146, n25 1.48892. Usual purification is by washing with several small portions of conc H2SO4 (until the acid layer is no longer coloured), then with water, 10% aq Na2C03, again with water, and drying with MgS04, MgC03 or Na2S04, followed by fractional distn. It can then be dried with, and distd from, Na, NaH or CaH2. Passage through columns of alumina or silica gel removes oxidation products. Has also been steam distd from 3% NaOH, and azeotropically distd with 2-ethoxyethanol (which was subsequently removed by washing out with water). Cumene hydroperoxide [ 8 0 - 1 5 - 9 1 M 152.2, b 60°/0.2mm, d 1.028, n24 1.5232. Purified by adding lOOml of 70% material slowly and with agitation to 300ml of 25% NaOH in water, keeping the temperature below 30°. The resulting crystals of the sodium salt were filtered off, washed twice with 25 ml portions of benzene, then stirred with lOOml of benzene for 20min. After filtering off the crystals and repeating the washing, they were suspended in lOOml of distilled water and the pH was adjusted to 7.5 by addn of 4M HCI. The free hydroperoxide was extracted into two 20ml portions of n-hexane, and the solvent was evaporated under vacuum at room temperature, the last traces being removed at 40-50° and lmm [Fordham and Williams Canad J Res 27B 943 19491. Petroleum ether, but not ethyl ether, can be used instead of benzene, and powdered solid C02 can replace the 4M HCl. The material is potentially EXPLOSIVE.

Purification of Organic Chemicals

155

Cuminaldehyde (4-isopropylbenzaldehyde) [ 1 2 2 - 0 3 - 2 1 M 148.2, b 82-84°/3.5mm, 120°/23mm, 131-135°/35mm, 235-236°/760mm, d20 0.978, nko 1.5301. Likely impurity is the benzoic acid. Check the IR for the presence of OH from C02H and the CO frequencies. If acid is present then dissolve in Et20, wash with 10% NaHC03 until effecrvescence ceases, then with brine, dry over CaC12, evap and distil the residual oil, preferably under vacuum. It is almost insoluble in H20, but soluble in EtOH and Et20. The thiosemicarbazone has m 147' after recrystn from aqueous EtOH, or MeOH or C6H6. [Crounse JACS 71 1263 1949; Bernstein et al. JACS 73 906 1951; Gensler and Berman JACS 80 4949 19581. Cupferron [135-20-61 M 155.2, m 162.5-163.5O. ether and air dried.

Crystd from EtOH (charcoal), washed with ethyl

Cuprein [524-63-01 M 310.4, m 202O, [(XI: -176O (in MeOH). Crystd from EtOH. Cuproin see 2,2'-biquinolyl. Curcumin [458-37-71 M 368.4, m 1 8 3 O . Crystd from EtOH or acetic acid. Cyanamide [420-04-21 M 42.0, m 41O. Crystd from ethyl ether, then vacuum distd at 80' (370mm). Hygroscopic. Cyanoacetamide [107-91-51 M 84.1, m 119.4O. Crystd from MeOH/dioxane (6:4), then water. Dried over P2O5 under vacuum. Cyanoacetic acid [372-09-81 M 85.1, m 70.9-71.1O. benzene/acetone (2:3), and dried over silica gel.

Crystd to constant melting point from

Cyanoacetic acid hydrazide [140-87-41 M 99.1, m 114.5-115O. Crystd from EtOH. 4-Cyanoacetophenone

see 4-acetylbenzonitrile.

p-Cyanoaniline [873-74-51 M 118.1, m 85-87O. Crystd from water, or EtOH, and dried in a vacuum for 6h at 40'. [Edidin et al. JACS 109 3945 1987. 9-Cyanoanthracene [1210-12-41 M 203.2, m 134-137O. Purified by crystn from EtOH or toluene, and vacuum sublimed in the dark and in an inert atmosphere [Ebied et al. JCSFT I 7 6 2170 1980; Kikuchi et al. JPC 91 574 19871. 9-Cyanoanthracene photodimer [33998-38-81 M 406.4. Purified by dissolving in the minimum amount of CHC13 followed by addition of EtOH [Ebied et al. JCSFT 1 75 1111 1979; 76 2170 19801. p-Cyanobenzoic acid [619-65-81 M 147.1, m 219O. Crystd from water. 4-Cyanobenzoyl chloride [6068-72-01 M 165.6, m 68-70°,69-700, 73-74O, b 132°/8mm, 150-151°/25mm. If the IR shows presence of OH then treat with SOC12 boil for lh, evaporate and distil in vacuum. The distillate solidifies and can be recrystallised from pet ether. It is moisture sensitive and is an irritant. [Ashley et a]. JCS 103 1942; Fison et al. JOC 16 648 19511. Cyanoguanidine [461-58-51 M 84.1, m 209.5O. Crystd from water or EtOH. 5-Cyanoindole [I5861-24-21 M 142.2, m 104-104O, 106-108O, 107-408O. Dissolve in 95% EtOH boil in the presence of charcoal, filter, evaporate to a small volume and add enough H20 to cause crystallisation and cool. Recrystd directly from aqueous EtOH and dried in a vacuum. UV: Lax 276 nm (log E 3.6) in MeOH. [Lindwall and Mantell JOC 18 345 1953,20 1458 1955; Thesing at al. B 95 2205 1962; NMR: Lallemend and Bernath Bull SOCChim France 4091 19701.

156

Purification of Organic Chemicals

p-Cyanophenol [767-00-0]M 119.1, m 113O. Crystd from pet ether, benzene or water and kept under vacuum over P2O5. [Bernasconi and Paschelis JACS 108 2969 19861. 3-Cyanopyridine [IOO-54-91M 104.1, m 50°. Crystd to constant melting point from o-xylenelhexane. 4-Cyanopyridine [IOO-48-11M 104.1, m 76-79O. Crystd from dichloromethane/ethyl ether mixture. Cyanuric acid [108-80-5] M 120.1, m >300°. Crystd from water. Dried at room temperature in a desiccator under vacuum. Cyanuric chloride [108-77-01M 184.4, m 154O. Crystd from CCl4 or pet ether (b 90-100°), and dried under vacuum. Recrystd twice from anhydrous benzene immediately before use [Abuchowski et al. JBC 252 3582 1977. Cyclobutane carboxylic acid [3721-95-71M 100.1, m 3-4O, -5.4O, b 84-84S0/10mm, 1 10°/25mm, 135-138°/110mm, 194O/760mm, d i 0 1.0610, n y 1.4534. Dissolve in aqueous HC03 and acidify with HCl and extract into Et20, wash with H20, dry (Na2S04), concentrate to a small volume, then distil through a glass helices packed column. It has a pKa25 of 4.79 in H20. The Sbenzylthiouronium salt has m 176O (from EtOH), and the anilide has m 112.5-1 13O, and the p-toluide has m 123O. [Payne and Smith JOC22 1680 1957; Kantaro and Gunning JACS 73 480 19-51].

trans-Cyclobutane-l,2-dicarboxylicacid [I 124-13-61M 144.1, m 131O. Crystd from benzene. Cyclobutanone [1191-95-3]M 70.1, b 96-97O, d 0.931, nS2 1.4189. Treated with dilute aqueous KMn04, dried with molecular sieves and fractionally distd. Purified via the semicarbazone, then regenerated, dried with CaS04, and distd in a spinning-band column. Alternatively, purified by preparative gas chromatography using a Carbowax 20-M column at 80°. (This treatment removes acetone). Cyclobutylamine [2516-34-91M 71.1, b 82-83O/atm, 83.2-84.2°/760mm, d i O0.839, nfDO 1.437. It has been purified by steam distn. The aqueous distillate (e.g. 2L) is acidified with 3N HCI (9Oml) and evapd to dryness in a vacuum. The hydrochloride is treated with a few ml of H20, cooled in ice and a slush of KOH pellets ground in a little H20 is added slowly in portions and keeping the soln very cold. The amine separates as an oil from the strongly alkaline soln. The oil is collected dried over solid KOH and distd using a vac jacketed Vigreux column and protected from C02 using a soda lime tube. The fraction boiling at 79-83O is collected, dried over solid KOH for 2 days and redistd over a few pellets of KOH (b 80.5-8 1So).Best distil in a dry N2 atmosphere. The purity can be checked by GLC using a polyethylene glycol on Teflon column at 72O, 15 psi, flow rate of 102 ml/min of He. The sample can appear homogeneous but because of tailing it is not possible to tell if H20 is present. The NMR in CCl4 should show no signals less than 1 ppm from TMS. The hydrochloride has a multiplet at ca 1.5-2.6ppm (H 2,2,4,3,3,4,4), a quintet at 3.8 ppm (H 1) and a singlet at 4.75 for NH2. It has a pKa25 of 9.34 in 50% aq EtOH [Roberts and Chambers JACS 73 2509 19511. The benzenesulphonamide has m 85-86O (from aq MeOH) and the benzoyl derivative has m 120.6-121.6O [Roberts and Mazur JACS 73 2509 1951;Iffland et al. JACS 75 4044 1953;Org Synth Coll Vol V 273 19731. Cyclodecanone [I 502-06-31M 154.2, m 21-24O, b 100-102°/12mm. Purified by sublimation. cis-Cyclodecene [935-31-91 M 138.3, m -3O, - l o , b 73O/15mm, 90.3O/33mm, 19419S0/740mm, 197-199O/atm, d i O0.8770, nLo 1.4854. Purified by fractional distn. It forms an A g N 0 3 complex which crystallises from MeOH, m 167-187O [Cope et al. JACS 77 1628 1955; IR: Blomqvist et al. JACS 74 3636 1952;Prelog et al. HCA 35 1598 19521. or-Cyclodextrin (HzO) [10016-20-31M 972.9, m >280°(dec), [~t]2504~ +175O (c 10, HzO). Recrystd from 60% aq EtOH, then twice from water, and dried for 12h in a vacuum at 80°. Also purified by pptn from water with 1,1,2-trichloroethylene. The ppte was isolated, washed and resuspended in water. This was boiled to steam distil the trichloroethylene. The soln was freeze-dried to recover the cyclodextrin. [Armstrong et al. JACS 108 1418 19861.

157

Purification of Organic Chemicals

P-Cyclodextrin ( H 2 0 ) [7585-39-91 M 1135.0, m >300°(dec), [ct]250q6 + 1 7 0 ° (c 10, H 2 0 ) . Recrystd from water and dried for 12h in vacuo at 1loo. The purity was assessed by TLC on cellulose with a fluorescent indicator. [Taguchi, JACS 108 2705 1986; Tabushi et al. JACS 108 4514 19861.

trans-cis-cis-1,5,9-Cyclododecatriene (cyclododec-lc,5c,9t-triene) [2765-29-91 M 162.3, m -9O, -So, b 117.5°/2mm, 237-239O/atm, 244O/760mm, dto 0.907, n;' 1.5129. Purified by fractional distn, preferably in a vacuum under Nz, and forms an insoluble AgN03 complex. [Breil et al. Makromol. Chemie 69 28 19631. Cyclododecylamine [1502-03-01 M 183.3, m 27-29O, b 140-150°/ca 18mm, 280°/atm. It can be purified via the hydrochloride salt m 274-275O (from EtOH) or the picrate m 232-234O, and the free base is distd at water-pump vacuum. Its pKa in 80% methyl cellosolve is 9.62. [Prelog et al. HCA 33 365 19501. 1,3-Cycloheptadiene [4054-38-01 M 94.2, b 55O/75mm, 71.5°/150mm, 120-121°/atm, d;' 0.868, nk'1.4972. It was purified by dissolving in Et20, wash with 5% HCl, H20, dry (MgS04), evap and the residue is distd under dry N2 through a semi-micro column (some foaming occurs), [Cope et al. JACS 79 6287 1957; UV: Pesch and Friess JACS 72 5756 19501. Cycloheptane [ 2 9 1 - 6 4 - 5 1 M 98.2, b 114.4O, d 0.812, n 1.4588. nitrogen.

Distd from sodium, under

Cycloheptanone [ 5 0 2 - 4 2 - 1 1 M 112.2, b 105°/80mm, 172.5OI760, d 0.952, nt4 1.4607. Shaken with aq KMnO4 to remove material absorbing around 230-240nm, then dried with Linde type 13X molecular sieves and fractionally distd. Cycloheptatriene [544-25-21 M 92.1. b 114-115O, d 0.895, n 1.522. Washed with alkali, then fractionally distd.

Cycloheptimidazole see 1,3-diaza-azulene. Cycloheptylamine [5452-35-71 M 113.2, b 50-52°/11mm, 60°/18mm, diO0.887, n y 1 . 4 7 2 . It can be purified by conversion to the hydrochloride m 242-246O, and the free base is distd under dry N2 in a vacuum. It has a pKaZ4 of 9.99 in 50% methyl cellosolve. [Cope et al. JACS 75 3212 1953; Prelog et al. HCA 33 365 19501. 1,3-Cyclohexadiene [592-57-41 M 80.1, b

83-&I0/atm. d;'

0.840, n;'

1.4707.

Distd from

Nab.

1,4-Cyclohexadiene [ 6 2 8 - 4 1 - 11 80.1, b 83-86°/714mm, 88.3°/741mm, 86-8S0/atm, , 88.789°/760mm, di0 0.8573, n',' 1.4725. Dry over CaC12 and distil in a vacuum under N2. [Hiickel and Worffel b 88 338 1955; Giovannini and Wegmuller HCA 42 1142 19591. Cyclohexane [ 1 1 0 - 8 2 - 7 1 M 84.2, f.p. 6.6O, b 80.7O, d24 0.77410, n 1.42623, n25 1.42354. Commonly, washed with conc H2SO4 until the washings are colourless, followed by water, aq NazC03 or 5% NaOH, and again water until neutral. It is next dried with P2O5, Linde type 4A molecular sieves, CaC12, or MgS04 then Na and distd. Cyclohexane has been refluxed with, and distd fiom Na, CaHz, LiAlH4 (which also removes peroxides), sodium/potassium alloy, or P205. Traces of benzene can be removed by passage through a column of silica gel that has been freshly heated: this gives material suitable for ultraviolet and infrared spectroscopy. If there is much benzene i n the cyclohexane, most of it can be removed by a preliminary treatment with nitrating acid (a cold mixture of 30ml conc HNO3 and 70ml of conc HzS04) which converts benzene into nitrobenzene. The impure cyclohexane and the nitrating acid are placed in an ice bath and stirred vigorously for 15min, after which the mixture is allowed to warm to 2 5 O during lh. The cyclohexane is decanted, washed several times with 25% NaOH, then water dried with CaC12, and distd from sodium. Carbonyl-containing impurities can be removed as described for chloroform. Other purification procedures

158

Purification of Organic Chemicals

include passage through columns of activated alumina and repeated crystn by partial freezing. Small quantities may be purified by chromatography on a Dowex 710-Chromosorb W gas-liquid chromatographic column.

Cyclohexane butyric acid [ 4 4 4 1 - 6 3 - 8 1 M 170.3, m 31°, 26.5-28S0, b 136-139O/4mm. 169O/20mm, 188.8O/46mm. Distil through a Vigreux column, and the crystalline distillate is recrystd from pet ether. It has a pKaZ5of 4.95 in H20. The S-benzyfthiouroniurnsalt has m 154-155O (from EtOH) [Acra Chern Scand 9 1425 1955; English and Dayan JACS 72 4187 19501.

Cyclohexane-1,2-diaminetetraacetic acid (HzO; CDTA) [I3291 -61 - 71 M 364.4. Dissolved in aq NaOH as its discdium salt, then pptd by adding HCI. The free acid was filtered off and boiled with distd water to remove traces of HCl [Bond and Jones TFS 55 1310 19591. Recrystd from water and dried under vacuum.

truns-Cyclohexane-l,2-dicarboxylic acid [ 2 3 0 5 - 3 2 - 0 1 M 172.2, m 226-228O, 227.5-228O, 228-230.5O. It is purified by recrystn from EtOH or H20. The dirnerhyl ester has m 95-96O (from CgH6-pet ether). [Abell JOC 22 769 1957; Smith and Byrne JACS 72 4406 1950; Linstead et al. JACS 64 2093 19421. (+)-truns-1,2-Cyclohexanediol[1460-57-71 M 116.2, m 104O, 1OSo, 120°/14mm. Crystd from Me2CO and dried at 50° for several days. It can also be recrystd from CC14 or EtOAc and can be distilled. The 2,4-dinitrobenzoylderivative has m 179O. [Winstein and Buckles JACS 64 2780 19421.

truns-1,2-Cyclohexanediol[ I R , 2 R - ( - ) : 1072-86-21 [lS,2S-(+) : 57794-08-81 M 116.2, m 107109O, 109-110S0, 109-111°, 111-112O, 113-114O, [a]L2k46S0 (c 1, HzO). The enantiomers have been recrystd from C6H6or EtOAc. The (f) diol has been resolved as the distrychnine salt of the hemisulphate [Hayward, Overton and Whitham JCS Perkin Trans I 2413 19761;or the I-rnenthoxyacerates. {dtrans- diastereoisomer has m 64O, [ a ] -91.7O ~ ) (c 1.4 EtOH) from pet ether or aqueous EtOH and yields the (-)trans-diol ) and (I-trans-diastereoisomer has m 126-127O, [ a ] -32.7O ~ ) (c 0.8 EtOH) from pet ether or aq EtOH and yields the (+)-trans diol). The bis-4-nirrobenzoare has m 126.5O [ a ]f 2~5 S 0 (c 1.1 CHC13), and the bis3,5-dinitrobenzoatehas m 160° [ a ] D f -83.0° (c 1.8 CHC13) [Wilson and Read JCS 1269 19351. cis-1,3-Cyclohexanediol [931-17-91 M 116.2, m 86O. Crystd from ethyl acetate and acetone. truns-1,3-Cyclohexanediol [5515-64-01M 116.2, m 117O. Crystd from ethyl acetate. cis-1,4-Cyclohexanediol [556-58-9/ M 116.2, m 102.5O. Crystd from acetone (charcoal), then dried and sublimed under vacuum. Cyclohexane-1,3-dione [504-02-91 M 112.1, m 107-108O. Crystd from benzene. C y c l o h e x a n e - 1 , 4 - d i o n e [ 6 3 7 - 8 8 - 7 1 M 112.1, m 76-77O, 78O, 79S0, 79-80°, b 130133O/20mm, d:' 1.0861, nbo21.4576. Crystd from water, then benzene. It can also be recrystd from CHC13/pet ether or Et2O. It has been purified by distn in a vacuum and the pale yellow distillate which solidified is then recrystd from CCl4 (14.3 g/100 ml) and has m 77-79O. The di-sernicarbazone has m 231°, the dioxirne HCl has m 150° (from MeOH-C&) and the bis-2,4-dinitrophenylhydrazonem 240° (from PhN02). [Org Synth Coll Vol V 288 1973; IR: LeFevre and LeFevre JCS 3549 19561. Cyclohexane-1,2-dione dioxime (Nioxime) [ 4 9 2 - 9 9 - 9 1 M 142.2, m 189-190°. alcohollwater and dried in a vacuum at 40°.

Crystd from

1,4-Cyclohexanedione monoethylene acetal (1,4-dioxa-spiro[4,5]decan-8-one)[4746-97-81 M 156.2, m 70-73O, 73.5-74.5O. Recrystd from pet ether and sublimes slowly on attempted distillation. Also purified by dissolving in Et20 and adding pet ether (b 60-80°) until turbid and cool. [Gardner et al. JACS 22 1206 1957; Britten and Lockwood JCS Perkin Trans I 1824 19741.

Purification of Organic Chemicals

159

cis,cis-1,3,5-Cyclohexane tricarboxylic acid [16526-68-41 M 216.2, m 214-21S0, 216-218O. Purified by recrystn from toluene + EtOH or H20. It forms a 1.5 hydrate with m 216-218O, and a dihydrate at 1loo. Purified also by conversion to the triethyl ester b 217-218°/10mm, 151°/lmm and distillate solidifies on cooling, m 36-37O and is hydrolysed by boiling in aq HCl. The trimethyl ester can be distd and recrystd from Et20, m 48-49O. [Newman and Lawrie JACS 76 4598 1954,Lukes and Galik Coll Czech Chem Comm 19 712 19541. Cyclohexanol [108-93-01M 100.2, m 25.2O, b 161.1°, d 0.9459, n 1.466, n25 1.4365, n30 1.4629. Refluxed with freshly ignited CaO, or dried with Na2C03, then fractionally distd. Redistd from Na. Further purified by fractional crystn from the melt in dry air. Peroxides and aldehydes can be removed by prior washing with ferrous sulphate and water, followed by distillation under nitrogen from 2,4dinitrophenylhydrazine, using a short fractionating column: water distils as the azeotrope. Dry cyclohexanol is very hygroscopic. Cyclohexanone [108-94-11 M 98.2, f.p. -16.4O, b 155.7O, d 0.947, n15 1.45203. n 1.45097. Dried with MgS04, CaS04, Na2S04 or Linde type 13X molecular sieves, then distd. Cyclohexanol and other oxidisable impurities can be removed by treatment with chromic acid or dil KMn04. More thorough purification is possible by conversion to the bisulphite addition compound, or the semicarbazone, followed by decompn with Na2C03 and steam distn. [For example, equal weights of the bisulphite adduct (crystd from water) and Na2C03 are dissolved in hot water and, after steam distn, the distillate is saturated with NaCl and extracted with benzene which is then dried and the solvent evaporated prior to further distn]. Cyclohexanone oxime [IOO-64-11M 113.2, m 90°. Crystd from water or pet ether (b 60-80°). Cyclohexanone phenylhydrazone [946-8271 M 173.3, m 77O. Crystd from EtOH. Cyclohexene [110-83-8]M 82.2, b 83O, d 0.810, n 1.4464, n25 1.4437. Freed from peroxides by washing with successive portions of dil acidified ferrous sulphate, or with NaHS03 soln then with distd water, dried with CaC12 or CaS04, and distd under N2. Alternative methods of removing peroxides include passage through a column of alumina, refluxing with sodium wire or cupric stearate (then distilling from sodium). Diene is removed by refluxing with maleic anhydride before distg under vac. Treatment with 0.lmoles of MeMgI in 4Oml of ethyl ether removes traces of oxygenated impurities. Other purification procedures include washing with aq NaOH, drying and distg under N2 through a spinning band column; redistg from CaH2; storage with sodium wire; and passage through a column of alumina, under N2, immediately before use. Stored in a refrigerator under argon. [Woon et al. JACS 108 7990 1986;Wong et al. JACS 109 3428 19871. (+)-2-Cyclohexen-l-oI (3-hydroxycyclohex-1-ene) [822-67-31M 242.2, b 63-65i0/12mm, 65-66O/13mm, 67O/15mm, 74O/25mm, 85[O/35mm, 166O/atm, d i 0 0.9865, n y 1 . 4 7 2 0 . Purified by distillation through a short Vigreux column. The 2,4-dinitrobenzoyl derivative has m 120S0, and the phenylurethane has m 107O. [Org Synth Coll Vol 48 18 1968, Cook J C S 1774 1938; Deiding and Hartman JACS 75 3725 19.531. Cyclohexene oxide [286-20-41M 98.2, b 131-133O/atm, di0 0.971, n;' 1.452. Fractionated through an efficient column. The main impurity is probably H20. Dry over MgS04, filter and distil several times (b 129-134O/atm). The residue is sometimes hard to remove from the distilling flask. To avoid this difficulty, add a small amount of a mixture of ground NaCl and Celite (1: 1) to help break the residue particularly if H20 is added. [Org Synth Coll Vol I 185 1948). Cycloheximide [68-81-91M 281.4, m 119.5-121O. Crystd from water/MeOH (4:l), amyl acetate, isopropyl acetate/isopropyl ether or water. Cyclohexylamine [108-91-81M 99.2, b 134S0, d 0.866, d25 0.8625, n 1.45926, n25 1.4565. Dried with CaC12 or LiAlH4, then distd from BaO, KOH or Na, under N2. Also purified by conversion to the hydrochloride, several crystns from water, then liberation of the amine with alkali and fractional distn under N2.

160

Purification of Organic Chemicals

Cyclohexylbenzene [827-52-11 M 160.3, f.p. 6.8O, b 237-239O, d 0.950, n 1.5258. by fractional distn, and fractional freezing.

Purified

Cyclohexyl bromide [108-85-0] M 156.3, b 72O/29mm, d 0.902, n25 1.4935. Shaken with 60% aqueous HBr to remove the free alcohol. After separation from excess HBr, the sample was dried and fractionally distd. Cyclohexyl chloride [542-18-71 M 118.6, b 142-142S0, d 1.000, n 1.462. Dried with CaC12 and distd. 1-Cyclohexyl-ethylamine IS-( +): 17430-98-71 [R-(-): 5913-13-31 M 127.2, b 177-178O/atm, d:' 0.866, n v 1.4463, [a]',5+3.2O (neat). Purified by conversion to the bitartrate salt (m 172O), then decomposing with strong alkali and extracting into Et20, drying (KOH), filtering, evaporating and distilling. The hydrochloride salt has m 242O (from EtOH-Et20), [ag5 -5.0° (c 10 H20; from (+) amine). The oxalate salt has m 132O (from H20). The (?)-base has b 176-178°/760mm, and HCI has m 237-238O. [Reihlen, Knopfle and Sapper A 532 247 1938; B 65 660 19321. Cyclohexylidene fulvene [3141-04-61 M 134.2. Purified by column chromatography and eluted with n-hexane [Abboud et al. JACS 109 1334 1987. Cyclohexyl mercaptan (cyclohexane thiol) [ I 5 6 9 - 6 9 - 3 1 M 116.2, b 38-39O/ 1 2 m m , 57O/23mm, 90°/100mm, 157O/763mm, d:' 0.9486, n;' 1.4933. Possible impurities are the sulphide and the disulphide. Purified by conversion to the Na salt by dissolving in 10% aq NaOH, extract the sulphide and disulphide with Et20, and then acidify the aq soln (with cooling and under N2) with HCl, extract with Et20, dry MgS04, evaporate and distil in a vacuum (b 4I0/12mm). The sulphide has b 74O/0.2rnm, I$*.~ 1.5162 and the disulphide has b 110-1 12O/0.2mrn, $ 1.5557. The Hg-rnercaptide has m 77-78O (needles from EtOH). [Naylor JCS 1532 1947. Cyclohexyl methacrylate [ I O I - 4 3 - 9 1 M 168.2, b 81-86°/0.1mm, d 0.964, n 1.458. Purification as for methyl methacrylate. 1-Cyclohexyl-5-methyltetrazole [7707-57-51 M 166.2, m 124-124.5O. EtOH, then sublimed at 115O/3mm.

Crystd from absolute

Cycloleucine see 1-amino-1-cyclopentanecarboxylic acid. Cyclononanone [3350-30-91 M 140.2, m 142.0-142.S0, b 220-222O. Repeatedly sublimed at 0.05O.lmm pressure. cis,cis-1,3-Cyclooctadiene [29965-97-71 M 108.2; [1,3-cyclooctadiene, [ I 700-10-31 M 108.21, m -So, -49O, b 5S0/34mm, 142-144°/760mm, d;' 0.8690, n y 1.48921. Purified by GLC. Fractionally distd through a Widmer column as a mobile liquid and redistilled with a Claisen flask or through a semi-micro column (Could, Holzman and Neiman A C 20 361 19481. NB: It has a strong characteristic disagreeable odour dectectable at low concentrations and causes headaches on prolonged exposure. [IR: Cope and Estes JACS 72 1128 1950; U V : Cope and Baumgardner JACS 78 2812 19561. cis-cis-l,S-cyclooctadiene, [1552-12-11 M 108.2, m -69S0, -70°, b 51-52°/25mm, 97°/144mm,150.80/757mm, di0 0.880, n i o 1.4935, Purified by GLC. It has been purified via the AgN03 salt. This is prepared by shaking with a soln of 50% aq AgN03 w/w several times (e.g. 3 x 50 ml and 4 x 50 ml) at 70° for ca 20min to get a good separation of layers. The upper layers are combined and further extracted with AgN03 at 40° (2 x 20 ml). The upper layer (19 ml) of original hydrocarbon mixture gives colourless needles AgN03 complex on cooling. The adduct is recrystd from MeOH (and cooling to OO). The hydrocarbon is recovered by steam distilling the salt. The distillate is extracted with Et20, dried (bigso& evap and distd. [Jones JCS 312 19541.

.

Purification of Organic Chemicals

161

Cyclooctanone [502-49-81 M 126.2, m 42O. Purified by sublimation after drying with Linde type 13X molecular sieves.

1,3,5,7-Cyclooctatetraene [629-20-91 M 104.2, b 141-141.5O,d 1.537, n25 1.5350. Purified by shaking 3ml with 2Oml of 10% aqueous AgN03 for 15min, then filtering off the silver nitrate complex as a ppte. The ppte was dissolved in water and added to cold conc ammonia to regenerate the cyclooctatetraene which was fractionally distd under vacuum onto molecular sieves and stored at 00. It was passed through a dry alumina column before use [Broadley et al. JSCDT 373 19861. c i s - C y c l o o c t e n e [ 9 3 1 - 8 8 - 4 1 M 110.2, b 32-34O/12mm, 66.5-67O/60mm, 88°/141mm, 140°/170mm, 143°/760mm, d i O 0.84843, n y 1.4702, The cis-isomer was freed from the transisomer by fractional distn through a spinning-band column, followed by preparative gas chromatography on a Dowex 710-Chromosorb W GLC column. It was passed through a short alumina column immediately before use [Collman et al. JACS 108 2588 19861. It has also been distd in a dry nitrogen glove box from powdered fused NaOH through a Vigreux column and then passed through activated neutral alumina before use [Wong et al. JACS 109 4328 19871. Alternatively it can be purified via the AgN03 salt. This salt is obtained from crude cyclooctene (40 ml) which is shaken at 70-80° with 50% w/w AgN03 (2 x 15 ml) to remove cyclooctadienes (aq layer). Extraction is repeated at 40° (4 x 20 ml, of 50% AgN03). Three layers are formed each time. The middle layer contains the AgNO3 adduct of cyclooctene which crystallises on cooling the layer to room temperature. The adduct (complex 2:l) is highly soluble in MeOH (at least lg/ml) from which it crystallises in large flat needles when cooled at Oo. It is dried under slight vacuum for 1 week in the presence of CaC12 and paraffin wax soaked in the cyclooctene. It has m 5 l o and loses hydrocarbon on exposure to air. cisCyclooctene can be recovered by steam distn of the salt, collected, dried (CaC12) and distilled in vacuum. [Braude et al. JCS 471 1 1957; AgN03: Jones JCS 1808 1954; Cope and Estes JACS 72 1128 19501.

.

cis-Cyclooctene oxide ((1r,8c)-9-oxabicyclo[6.1.0]nonane} [ 2 8 6 - 6 2 - 4 1 M 126.7, m 56-57O, 57.5-57.8O,5O-6O0,b 85-8S0/17mrn,82S0/22mm, 90-93O/37mm, 189-190°/atm. It can be distd in vacuum and the solidified distillate can be sublimed in vacuum below 50°. It has a characteristic odour. [IR: Cope et al. JACS 74 5884 1952, 79 3905 1957; Reppe et al. A 560 1 19481. Cyclopentadecanone [502-72-71 M 224.4, m 63O. Sublimation is better than crystn from aq EtOH. Cyclopentadiene [542-92-71 M 66.1, b 41-42O. Dried with Mg(C104)2 and distd. Cyclopentane [ 2 8 7 - 9 2 - 3 1 M 70.1, b 49.3O, d 0.745, n 1.40645, n25 1.4340. Freed from cyclopentene by two passages through a column of carefully dried and degassed activated silica gel. Cyclopentane carbonitrile [ 4 2 5 4 - 0 2 - 8 1 M 95.2, m -75.2O, -76O, b 43-44O/7mm, 5062°/10mm, 67-68O/14mm, 74.5-75°/30mm, d i 0 0.912, n i o 1.441. Dissolve in Et20, wash thoroughly with saturated aqueous K2CO3, dry (MgS04) and distil through a 10 cm Vigreux column. [McElvain and Stem JACS 77 457 1955, Bailey and Daly 81 5397 19591.

Cyclopentane-1,l-dicarboxylic acid [5802-65-31 M 158.1, m 184O. Recrystd from water. 1,3-Cyclopentane-dione [ 3 8 5 9 - 4 1 - 4 1 M 98.1, m 149-150°, 151-152.5°,151-1540,151-153O. Purified by Soxhlet extraction with CHC13. The CHC13 is evaporated and the residue is recrystd from EtOAc and/or sublimed at 120°/4mm. It has an acidic pKa of 4.5 in H20. [IR: Boothe et al. JACS 75 1732 1953; DePuy and Zaweski 81 4920 19591. Cyclopentanone ( 1 2 0 - 9 2 - 3 1 M 84.1, b 130-130S0,d 0.947, n 1.4370, n25 1.4340. Shaken with aq KMn04 to remove materials absorbing around 230 to 240nm. Dried with Linde type 13X molecular sieves and fractionally distd. Has also been purified by conversion to the NaHS03 adduct which, after crystallising four times from EtOWwater (4: I), was decomposed by adding to an equal weight of Na2C03 in hot H20. The free cyclopentanone was steam distd from the soln. The distillate was saturated with NaCl and

162

Purification of Organic Chemicals

extracted with benzene which was then dried and evaporated; the residue was distd [Allen, Ellington and Meakins JCS 1909 19601.

Cyclopentene [142-29-01 M 68.1, b 45-46O, d 0.772, n 1.4228. Freed from hydroperoxide by refluxing with cupric stearate. Fractionally distd from Na. Chromatographed on a Dowex 710-Chromosorb W GLC column. Methods for cyclohexene should be applicable here. Also washed with 1M NaOH s o h followed by water. It was dried over anhydrous Na2S04, distd over powdered NaOH under nitrogen, and passed through neutral alumina before use [Woon et al. JACS 108 7990 19861. It was distd in a dry nitrogen atmosphere from powdered fused NaOH through a Vigreux column, and then passed through activated neutral alumina before use [Wong et al. JACS 109 3428 1987.

l-Cyclopentene-1,2-dicarboxylic anhydride [3205-94-51 M 138.1, m 42-54O, 46-47O, b 130°/5mm, 133-135O/5mm, nio 1.497. If IR has OH peaks then some hydrolysis to the diacid (m 178O) must have occurred. In this case reflux with an appropriate volume of Ac20 for 30min, evaporate the Ac2O and distil in vacuo. The distillate solidifies and can be recrystd from EtOAc-hexane (1: 1). The diacid distils without dec due to formation of the anhydride. The dime ester has m 120-125O/1lmm. [Askain B 98 2322 19651. Cyclopentylamine [1003-03-81 M 85.2, m -85.7O, b 106-108°/760mm, 108.5°/760mm, di0 0.8689, n y 1.4515. May contain H20 or C02 in the form of carbamate salt. Dry over KOH pellets and then distil from a few pellets of KOH. Store in a dark, dry C02-free atmosphere. It is characterised as the thiocyanate salt m 94.51~.It has a pKaZ5in 50% aa EtOH of 4.05. The benzenesulphonyl derivative has m 68.5-69.5O. [Roberts and Chambers JACS 73 5030 1951; Bollinger et al. JACS 75 172919531. Cyclopropane [75-19-41 M 42.1, b - 3 4 O . Washed with a soln of HgS04, and dried with CaC12, then Mg(C104)2. Cyclopropanecarbonyl chloride [4023-34- I ] M 104.5, b 117.9-118.0°/723mm, 119.5119.6[0/760mm, d i 0 1.142, n :o 1.453. If the IR shows OH bands then some hydrolysis to the free acid must have occurred. In this case heat with oxalyl chloride at 50° for 2h or SOC12 for 30min, then evap and distil three times using a Dufton column. Store in an inert atm, preferably in sealed tubes. Strong irritant If it is free from OH bands then just distil in vacuo and store as before. [Jeffrey and Vogel JCS 1804 19481. Cyclopropane-1,l-dicarboxylicacid

[598-10-71 M 130.1, m 140O. Recrystd from CHC13.

Cyclopropylamine [765-30-01 M 57.1, b 49-49S0/760mm, 48-50°/atm, 49-50°/750mm, 1.421. It has been isolated as the benzamide m 100.6-101.Oo (from aqueous EtOH). dO ; 0.816, n It forms a picrate m 149O (from EtOH-pet ether) from which the free base can be recovered using a basic ion exchange resin and can then be distd through a Todd column using an automatic still head which only collects products boiling below 51°/atm. Polymeric materials if present will boil above this temperature. The hydrochloride has m 85-86O. The pKa25 in 40% EtOH is 5.33. [Roberts and Chambers JACS 73 5030 1951; Jones J O C 9 484 1944; Emmons JACS 79 6522 19571.

ko

Cyclopropyldiphenylcarbinol [5785-66-01 M 224.3, m 86-87O. Crystd from n-heptane.

Cyclopropyl methyl ketone [765-43-51 M 84.1, b 111.6-111.8°/752mm, d 0.850, n 1.4242. Stored with anhydrous CaS04, distd under nitrogen. Redistd under vacuum. R - and S- Cycloserine see R - and S- 4-amino-3-isoxazolidone see entry in Chapter 5.

Cyclotetradecane [295-17-0] M 192.3, m 56O. Recrystd twice from aq EtOH then sublimed in vacuo [Dretloff et al. JACS 109 7797 1987. Cyclotetradecanone [832-10-01 M 206.3, m 25O, b 145°/10mm, d 0.926, n 1.480. It was converted to the sernicarbazone which was recrystd from EtOH and reconverted to the free cyclotetradecanone by hydrolysis [Dretloff et al. JACS 109 7797 1983.

Purification of Organic Chemicals

163

Cyclotrimethylenetrinitramine (RDX) [121-82-41 M 222.2, m 203.S0(dec). Crystd from acetone. EXPLOSIVE. p-Cymene [99-87-6] M 134.2, b 177.1°, d 0.8569, n 1.4909, n25 1.4885. Washed with cold, conc H2SO4 until there is no further colour change, then repeatedly with H20, 10% aqueous Na2C03 and H20 again. Dried with Na2S04, CaC12 or MgS04, and distd. Further purification steps include steam distn from 3% NaOH, percolation through silica gel or activated alumina, and a preliminary refluxing for several days over powdered sulphur. Cystamine dihydrochloride, S,S-(L,L)-Cystathionine, Cysteamine and Cysteamine hydrochloride, (f)-Cysteic acid and S-Cysteic acid ( H 2 0 ) , L-Cysteine hydrochloride ( H 2 0 ) and (+)-Cysteine hydrochloride, L-Cystine, Cytidine, see entries in Chapter 5. Cytisine (7R,9S-7,9,10,11,12,13-hexahydro-7,9-methano-12H--pyrido[1,2-1][1,5]diazocin8-one, Laburnine Ulexine) [ 4 8 5 - 3 5 - 8 1 M 190.3, m 152-153O, 155O, b 21S0/2mm, [a]:' 25' -120O ( H 2 0 ) , [ a ] -115" ~ (c 1, HzO). Crystd from acetone and sublimed in a vacuum. It has pKa values of 6.1 1 and 13.08 in H20. Its solubilities are: 77% (H20), 7.7% (Me2CO , 28 6% (EtOH), 3.3% (C6H6), 50% 21 . (CHC13) but is insoluble in pet ether. The tartrate has m 206-207O [ a ] ~ +45.9O, the N-tosylate has m 206207O, and the N-acetate has m 208O. [Synthesis: Bohlmann et al. Angew Chemie 67 708 1955; van Tamelen and Baran JACS 77 4944 1955; Isolation: Ing J C S 2200 1931; Govindachari et al. JCS 3839 1957; Abs config: Okuda et al. Chemistry and Industry (London) 1751 19611. Cytosine see entry in Chapter 5.

DDT

see l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane.

Decahydronaphthalene (mixed isomers) [ 9 1 - 1 7 - 8 1 M 138.2, b 191.7O, d 0.886, n 1.476. Stirred with conc H2SO4 for some hours. Then the organic phase was separated, washed with water, saturated aqueous Na2CO3, again with water, dried with CaS04 or CaH2 (and perhaps dried further with Na), filtered and distd under reduced pressure (b 63-70°/10mm). Also purified by repeated passage through long columns of silica gel previously activated at 200-250°, followed by distn from LiAlH4 and storage under N2. Type 4A molecular sieves can be used as a drying agent. Storage over silica gel removes water and other polar substances. cis-Decahydronaphthalene [493-01-61 M 138.2, f.p. -43.2O, b 195.7O, d 0.897, n 1.48113, trans-Decahydronaphthalene [493-02-71 M 138.2, f.p. -30.6O, b 187.3O, d 0.870, n 1.46968. Purification methods described for the mixed isomers are applicable. The individual isomers can be separated by very efficient fractional distn, followed by fractional crystn by partial freezing. The cis-isomer reacts preferentially with AlC13 and can be removed from the trans-isomer by stirring the mixture with a limited amount of AlClJ for 48h at room temperature, filtering and distilling. Decalin see decahydronaphthalene. Decamethylene glycol see decane-1,lO-diol. n-Decane [124-18-5] M 142.3, b 174.1°, d 0.770, n 1.41189, n25 1.40967. It can be purified by shaking with conc H2SO4, washing with water, aqueous NaHC03, and more water, then drying with MgS04, refluxing with Na and distilling. Passed through a column of silica gel or alumina. It can also be purified by azeotropic distn with 2-butoxyethanol, the alcohol being washed out of the distillate, using water; the decane is

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