Organic Syntheses, Coll. Vol. 4, p.491 (1963); Vol. 35, p.66 (1955).
The following operations should be carried out in an effective hood (Note 1)
In a 3-l. round-bottomed flask
are placed 380 g. (5 moles) of thiourea (Note 2)
, 500 ml. of water, and 400 ml. of concentrated hydrochloric acid (12.5N) (Note 3)
. The solid is dissolved by gentle heating, and the solution is cooled to 30°. Furfuryl alcohol (490 g., 434 ml., 5 moles) (Note 4)
is added to the reaction mixture. The reaction, which usually commences spontaneously within a few minutes (Note 5)
, is strongly exothermic and should be controlled by suitable cooling with tap water so as to hold the temperature near 60° (Note 6)
. When the reaction subsides, cooling is discontinued and the clear, dark green solution is allowed to stand at room temperature for 12 hours.
A solution of 225 g. of sodium hydroxide (Note 3)
in 250 ml. of water is poured into the reaction mixture. A heavy brown oil separates, consisting of S-2-furfurylisothiourea
, which has already partially decomposed to 2-furfuryl mercaptan
. The flask is quickly fitted with a steam-inlet tube and condenser
. Steam distillation is continued as long as the distillate contains oily drops. The mercaptan is separated from the aqueous phase by means of a separatory funnel (Note 7)
and (Note [*****note*****])
. The product is dried with calcium chloride
; yield 313–340 g.
). The 2-furfuryl mercaptan
so obtained is of a high degree of purity (Note 9)
but can be distilled without decomposition in a nitrogen
atmosphere; b.p. 160°/759 mm.
, 84°/65 mm.
The odor of the mercaptan is extremely disagreeable, and the substance in high concentration causes headache. An effective hood
is absolutely essential.
The checkers employed practical grade thiourea obtained from Matheson, Coleman and Bell, East Rutherford, New Jersey
The checkers employed practical grade furfuryl alcohol obtained from the Eastman Kodak Company
If the reaction does not start, the flask is heated gently until a spontaneous temperature rise sets in.
Temperatures above 60° and particularly supplementary refluxing are to be avoided since under these conditions the sensitive furan
ring is attacked.
The mercaptan is almost insoluble in water, and the aqueous phase contains too little product to justify extraction.
It is convenient to use a 2-l. separatory funnel
as a receiver during the steam distillation.
The checkers found the undistilled product to be essentially pure; nD25
1.5285. The distilled material was obtained with only mechanical losses; b.p. 84°/65 mm.
The formation of mercaptans directly from alcohols may be applied to the preparation of a large number of mercaptans, but usually much longer reaction periods or higher temperatures and higher concentrations of hydrogen halides are required.6
Under such conditions the furan
ring is destroyed.
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved