Howard M. Crosby and John B. Entrikin
An Improved Method for Preparing
Centenary College Shreveport, Louisiana
S-AIkyIis~thi~uronium Picrates
I t has been found that better yields of S-alkylisothiouronium picrate derivatives of primary and secondary alkyl halides may be obtained by the procedure given below than by the conventional method.' The reflux time required is much shorter and no sodium iodide need be added with alkyl chlorides. All attempts to make derivatives of tertiary alkyl halides failed. Although only a limited number of alkyl halides were tested, it is believed that this method has more general application. Certaiu compounds, particularly the primary alkyl iodides cause decomposition of the reaction mixture a t the recommended bath temperature of 117'C. However, the compounds that ,decompose a t 117' do form derivatives when the bath i s held a t 65", even though the higher temperature is required for most compounds tested. If decomposition occurs a t 117" (evidenced by a decided odor of mercaptans and a red coloration of the mixture), the experiment should be repeated with the bath held a t 65". Procedure. To an 8-in. test tube, add 300 mg of thiourea, 5 ml of ethylene glycol, 6 drops of the alkyl Presented at the 37th Annual Meeting of the Louisiana Academy of Sciences, April 27,1963. CHERONIS, N. D., AND ENTRIKIN, J. B., "Semimicro Qualitative Organic Analysis,'' 2nd ed., Interscience Publishers, New York, 1957, p. 456.
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Journal o f Chemical Education
halide, and 2 boiling stones. Preheat an oil bath to 117'C. After attaching a reflux condenser (finger) to the test tube, place the tube in the heated oil bath and maintain the bath a t 117" for 30 min. Add 1 ml of a saturated solution of picric acid in ethanol to the reaction tube and leave it in the oil bath for an additional 15 min. Remove the tube, cool it, and add 5 ml of cold water. Place the tube in an ice bath for 15 min (shaking it occasionally). The derivative is then filtered and recrystallized from methanol. The alkyl halides tested by the above procedure using bath temperatures of either 117 or 65OC are listed. The melting points (OC) of the S-alkylisothiouronium picrates obtained are given in parentheses after each compound. These data serve to distinguish between the two melting points reported for some of these derivatives (see footnote 1, p. 634). Bath temperature 117'C: 1-chlorobutane (177), 1-chloropentane (154) ; 1-chlorohexane (157) ; l-bromopropane (177) ; 1-bromo-2-methylpropane (167) ; 2-bromopropane (196) ; 2-bromobutane (166) ; l-iodo2-methylpropane (167); 2-octobutane (166). Bath temperature 65'C: 1-bromooctane (134); 1-iodoethane (188) ; 1-iodopropane (177) ; 1-iodobutane (177) ; 1-iodohexane (157).
