2.6- Dimethylphenylthiourea

Dimethylphenylthiourea, 46, 70 Dimethylphosphine, 46, 103 Dimethylphosphinic acid, 46, 103 Dimethylphosphinyl chloride, 46, 103 N,N-Dimethyl-l,3-propanediamine, reaction with ethyl isocyanate, 48, S3... 

Silicon tetraisothiocyanate (26.0 g., 0.10 mole) (Note 10) is finely ground under 100 ml. of anhydrous benzene, and the mixture is quickly transferred to a 1-1. round-bottomed flask. The mortar and pestle are washed with two 25-ml. portions of anhydrous benzene, and the washings are added to the flask. A solution of 2,6-dimethylaniline (48.5 g., 0.4 mole) (Note 1) in 100 ml. of anhydrous benzene is added to the well-stirred mixture. The reaction is mildly exothermic. The mixture is heated at the reflux temperature for 30 minutes, and the benzene is then removed using a rotary evaporator. Dilute isopropyl alcohol (200 ml.) (Note 5) is added to the residue, and the resulting mixture is heated at the reflux temperature for 30 minutes. The mixture is then processed in exactly the same manner as described above for the preparation of cyclohexylurea. The crude 2,6-dimethylphenylthiourea (m.p. 193-197°, 71.3 g., 99% yield) is recrystallized from 280 ml. of isopropyl alcohol (Note 8) to give 50 g. (72%) of product, m.p. 201-202°. Concentration of the mother liquor affords 11 g. (15%) of less pure product, m.p, 197-199° (Note 11). 

Dimethylphenylthiourea has been synthesized by allowing 2,6-dimethylaniline hydrochloride to react with ammonium thiocyanate.14... 

A soln. of cyclohexylamine in anhydrous benzene added slowly to a stirred soln. of silicon tetraisocyanate in the same solvent, refluxed 0.5 hr. after the exothermic reaction has subsided, the benzene removed by distillation, isopropanol containing up to 10% water added, and refluxed 0.5 hr. cyclo-hexylurea. Y 65-97%. — Similarly 2,6-Dimethylaniline and silicon tetraisothiocyanate 2,6-dimethylphenylthiourea. Y 72-99%. F. e. s. R. G. Neville and J. J. McGee, Org. Synth. 45, 69 (1965). 

PTH amino acid analyzers used in this study were Applied Biosystems (59/78), Hewlett-Packard (16/78), Beckman (2/78), and Waters (1/78). The average age of these instruments was 5.2 2.6 years, and nearly all (76/78) were on-line with the sequencing system. Most users of Applied Biosystems sequencers reported using premix buffers (49/57), and several reported using additives to adjust the baseline (22/57) or to improve yields (18/57). The most common additive to Applied Biosystems solvent A was acetone (13/57), while others reported adding tryptophan (2/57) and TEA (2/57). Several facilities use dimethylphenylthiourea (DMPTU) to adjust the baseline rise (12/57) and isopropanol to improve tryptophan resolution in Applied Biosystems solvent B. 

Figure 24.4 PTH amino acid standards run on a Procise instrument see Table 24.1 for amino acid abbreviations. Peaks marked dmptu (dimethylphenylthiourea) and dptu (diphenylthiourea) represent side-reaction products of the Edman degradation. Courtesy of Applied Biosystems.)...

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