A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1932, 12, 52
DOI: 10.15227/orgsyn.012.0052
[Pseudourea, 2-methyl-2-thio-, sulfate]
Submitted by P. R. Shildneck and Wallace Windus.
Checked by Henry Gilman and W. F. Schulz.
1. Procedure
In a 2-l. round-bottomed flask are mixed 152 g. (2 moles) of finely divided thiourea and 70 cc. of water. To this is added 138 g. (1.1 moles) of technical methyl sulfate (Note 1). The flask is immediately attached to a long reflux condenser carrying a trap. The reaction is allowed to progress spontaneously (Note 2), with occasional cooling as the reaction becomes more rapid and the flask becomes filled with vapor. After the initial vigorous reaction is completed, the mixture is refluxed for one hour, during which time crystallization takes place (Note 3). The mixture is then allowed to cool, the flask is removed, 200 cc. of 95 per cent ethyl alcohol is added, and the contents of the flask are then filtered with suction. The residue is washed twice with 100-cc. portions of 95 per cent alcohol and allowed to dry in air. The yield is 190 g. of a product which melts with decomposition at 235°. Another crop of crystals weighing 43 g. and melting at 230° can be obtained from the alcoholic filtrate by concentrating it to a paste to which, after cooling, is added 120 cc. of 95 per cent alcohol. The total yield is 220–233 g. (79–84 per cent of the theoretical amount).
2. Notes
1. Technical methyl sulfate, if it has not turned dark brown, need not be distilled before using.
2. If the mixture is cooled too much with ice water, the spontaneous reaction almost ceases and gentle heating is required to start the reaction again. If the mixture is not cooled, the initial vigorous reaction is so violent that material is likely to be lost through the condenser. Since methyl sulfate is poisonous, this must be avoided. Ammonia, which is a specific antidote for methyl sulfate, should be kept at hand.
The checkers observed no spontaneous reaction, and in order to initiate reaction the flask and contents were gently heated with a moving low flame. When reaction sets in, the flame is removed. A container with ice water is kept handy to moderate any unduly vigorous reaction, particularly if the water condenser is less than 125 cm. in length.
3. The completion of the vigorous reaction indicates that half of the thiourea is methylated and that the methyl sulfate has been converted to methylhydrogen sulfate. Vigorous heating is necessary to complete the methylation.
3. Discussion
The procedure described is essentially that of Arndt.1
This preparation is referenced from:

References and Notes
  1. Arndt, Ber. 54, 2236 (1921).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

ethyl alcohol,
alcohol (64-17-5)

ammonia (7664-41-7)

methyl sulfate,
methylhydrogen sulfate (75-93-4)

thiourea (62-56-6)

S-Methyl isothiourea sulfate,
Pseudourea, 2-methyl-2-thio-, sulfate (867-44-7)