Weygand/Hilgetag Preparative Organic Chemistry

226 Formation of carbon-halogen bonds
and 2-3 moles of pyridine cooled in ice or ice-salt; 1-1.1 moles of pyridine
and 1.1 moles of SOC12 are usually used per mole of alkynolor alkoxyalkanol,
or 1.3-1.4 moles of SOC12 for alkanols that are in danger of isomerization by
HC1. A larger excess of SOC12 (2 moles of SOC12 per mole of OH) is sometimes
recommended for w-alkyl chlorides, and even 4 moles of SOC12 — without
pyridine — for higher alkyl chlorides such as undecyl and dodecyl chloride. 901
The alcohols may be diluted with benzene, 944 CHC13, 921 or ether ; 435 ' 924 - 925
and for alkoxyalkanols dimethylaniline 919 " 921 or quinoline 920 may replace
pyridine. The SOC12 used should be purified (see below) or freshly distilled.
l-Chloropentane: 865 SOC12 (6.5 moles) is dropped into a mixture of 1-pentanol (5 moles)
and dry pyridine (5 moles) at —10°. The mixture is warmed to 104° during 6h and kept
at 104° for 90 min. Evolution of SO2 begins at about 70°. The crude product is cooled, washed
with dilute HC1, dried over K2CO3, and distilled, giving an 80% yield of material boiling
at 106-106.5°/741 mm.
l-Chloro-2-heptyne: 924 When a solution of the alkynol (1 mole) and dry pyridine (1 mole)
in dry ether (100 ml) is dropped into a stirred solution of SOC12 (1.1 moles) in dry ether
(100 ml) the exothermic reaction keeps the mixture at the boiling point. When the reaction
ceases, ether is distilled off until the internal temperature reaches 80° (about 150 ml), then
further SOC12 (13 g) is added and the whole is boiled and stirred for a further hour. Cold
water (500 ml) is added and the ethereal layer is separated, washed with sodium carbonate
solution, dried over CaCl2, and evaporated. The chloroheptyne (77 % yield), when rapidly
distilled in a vacuum, has b.p. 73°/24 mm.
2-Ethoxyethyl chloride (2-chloroethyl ethyl ether): 920 A mixture of a dry base (1 mole)
and 2-ethoxyethanol (1 mole) is cooled to —20° and SOC12 (1.1 mole) is added, with stirring,
at such a rate that the temperature does not exceed 0°. The mixture is allowed to come to
room temperature and then kept at 100° for 2 h. The product is cooled and treated with
dilute HC1, and the ethoxyethyl chloride is taken up in ether, washed with dilute NaOH
solution and with water, and dried over Na2S04. Yields are 61% (with dimethylaniline),
80% (with pyridine), and 84% (with quinoline).
2-Chloro-2-phenylacetic add: 945 Ethyl mandelate (0.75 mole; from mandelic acid and
ethanol-HCl) is dissolved in SOC12 (0.82 mole), and the solution is set aside at room temperature
for 16 h, heated on a water-bath for 30 min, and poured into ice-water. The ethyl
2-chloro-2-phenylacetate formed (81-85 % yield) is extracted with ether and, after isolation,
is hydrolysed by a boiling mixture of glacial acetic acid and concentrated hydrochloric acid.
Methyl 2-chloro-2-phenylacetate is obtained in poorer yield by adding POC13 (11.5 g)
portionwise to methyl mandelate (12.5 g) and pyridine (12 g) cooled in ice-salt, and further
reaction for 1 h in the cooling mixture and for 12 h at room temperature. 946
ot-Chlorodeoxybenzoin, C6H5CHC1COC6H5: The preparation from benzoin (0.47 mole),
pyridine (0.63 mole), and SOC12 (0.63 mole) is detailed in Organic Syntheses. 947
Purification of thionyl chloride: A method often used is to boil technical SOC12 with about
10% of linseed oil and then to distil it through a column. Distillation with quinoline has
also been recommended 948 for removal of impurities such as SO3 and H2SO4, but a warning
has been given 949 against using dimethylaniline. For instance, 50 g of SOC12 may be distilled
from 10 ml of quinoline and then from 20 ml of linseed oil. 950 The following simple process
is very useful: 951 Crude SOC12 (900 ml) and flowers of sulfur (25 g) are boiled together under
reflux for 4.5 h; rapid distillation through a column then gives 94% of a colored product
(sulfur monochloride, b.p. 135.6°, remains in the flask); this product is then redistilled through
a column in such a way that it gives a colored forerun (sulfur dichloride, b.p. 69°; etc.) in
12 h and then almost colorless SOC12 (88%), b.p. 78.8°, in about 2 h.
Disulfur dichloride may be removed by distillation from red phosphorus. 111
944 C. Barkovsky, Ann. Chim., 19, 487 (1944).
9 * 5 E. L. Eliel, M. T. Fisk, and T. Prosser, Org. Syn., 36, 3 (1956).
946 T. Wagner-Jauregg, Helv. Chim. Acta, 12, 63 (1929).
947 A. M. Ward, Org. Syn., Coll. Vol. II, 159 (1943).
948 H. Meyer and K. Schlegel, Monatsh. Chem., 34, 569 (1913).
949 E. Besthorn, Ber. Deut. Chem. Ges., 42, 2697 (1909).
950 E. L. Martin and L. F. Fieser, Org. Syn., Coll. Vol. II, 569 (1943).
951 D. L. Cottle, /. Amer. Chem. Soc, 68, 1380 (1946).