Benzylthiouronium salts

Arsonic acids, like carboxylic and sulphonic acids (pp. 349, 353), usually give crystalline benzylthiouronium salts. Add just sufficient dilute aqueous sodium hydroxide dropwise with shaking to a suspension of 0 5 g. of phenylarsonic acid in 10 ml. of water to give a clear solution. Then add 0 5 g. of benzylthiouronium chloride dissolved in 10 ml. of water. Filter off the precipitated benzylthiouronium salt, wash with water and dry m.p. 114-117° it tends to dissociate on attempted recrystallisation. 

A) Benzylthiouronium salts. The sodium salt of an acid in aqueous solution will react with benzylthiouronium chloride ... 

Example. Dissolve 0 3 g. of benzoic acid in a minimum of hot water (about 70 ml.) and add 5% aqueous sodium hydro.xide until the solution is just alkaline to methyl-orange, then add i drop of dilute hydrochloric acid. Pour this solution of the sodium salt into a solution of 0 5 g, of benzylthiouronium chloride in 5 ml. of water, and cool the stirred mixture in ice-water. Filter off the benzylthiouronium salt which has separated, and recrystallise from ethanol con taining 10% of water cream-coloured cr> stals, m.p. i66 . (M.ps., pp. 543 545.)... 

B) Benzylthiouronium salts. Cold aqueous solutions of ammonium... 

The preparation of the benzylthiouronium salt is clearly the more satisfactory. 

Benzylthiouronium salts. Add 0 5 g. of sulphanilic acid to 10 ml. of water and 5 ml. of 10% NaOH solution, zndgently warm the shaken mixture until a clear solution is obtained. Cool, add 1 drop of phenol-phthalein solution, and then add dilute HCl dropwise with shaking until the pink colour is just discharged. Now add very dilute NaOH solution until the pink colour yt/rZ returns. Cool and add with shaking a solution of 0-5 g. of benzylthiouronium chloride in 5 ml. of water. The thiouronium salt rapidly separates filter at the pump, wash with water, drain and recrystallise from ethanol. Colourless crystals, m.p. 185°. (M.ps., p. 548.)... 

Carboxylic Acids, Benzylthiouronium salts (p. 349), Phenacyl esters (p. 349), /(-Bromophenacyl esters (p. 349), N Benz lamides (p. 350), -Nitrobenzyl esters (p. 350). 

Ammonium Salts. Benzylthiouronium salts (p. 360), Acids if aromatic (p. 360), Benzylamides (p. 360). 

Sulphonic Acids. Benzylthiouronium salts (p. 359), Sulphonamides and sulphonanilides (p. 354). 

Hexafluorotropone is readily hydrolyzed in aqueous sodium hydroxide to give the three monohydroxy isomers [6] (equation 8) The major product is 1 hydroxy-pentafluorotropone, the other two isomers are formed in about equal quantities Separation of the 2- and 3-hydroxy isomers from the mixture is based on the ability of the 2-hydroxy isomer to form a cupric chelate, and of the 3-hydroxy isomer to precipitate as an 5 benzylthiouronium salt... 

Cyclohexane hutyric acid [4441-63-8] M 170.3, m 31 , 26.5-28.5 , h 136-139 74mm. 169 /20mm, 188,8 /46mm, Distil through a Vigreux column, and the crystalline distillate is recrystd from pet ether. It has a pKa of 4.95 in H2O. The S-benzylthiouronium salt has m 154-155 (from EtOH) [Acta Chem Scand 9 1425 1955-, English and Dayan JACS 72 4187 1950],... 

An interesting example of analysis based on formation of benzylthiouronium salts is the work of Muramoto and Hirao109. It is, in fact, quantitative analysis of binary mixtures of sulphonates, e.g. of o- and p-toluenesulphonates and other aromatic pairs. They measured the melting points of mixtures of the benzylthiouronium salts prepared from the samples and interpolated the values between those for the pure compounds. Muramoto110 extended it to further aromatic pairs. 

A. Friediger and C. Pedersen, S-benzylthiouronium salts, Acta Chem. Scand, 9 (1955) 1425-1430. S. Veibel and C. Pedersen, Syntheses des Esters Acides d Acides Dicarboxyliques par Action de I Alcoolates de Sodium ou de Potassium sur les Anhydrides d Acides Correspondants, Acta Chem. Scand., 9 (1955) 1674-1684. 

Aniline salt Cryst. (EtOH). Mp 116°. S-Benzylthiouronium salt Cryst. (EtOH). Mp 176° Me ester [18830-44-9]. 

S-Benzylthiouronium salt Cryst. -I- IOH2O. Mp 330° dec. Amide [27771-61-5]. 6-Amino-2-naphthalenesulfonamide Acid-base fluorescent indicator (pH range 1.9-3.9, colour change no fluorescence - blue pH range 9.6-... 

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