Thenoic Acid

Submitted by E. Campaigne and William M. LeSuer.1 Checked by Charles C. Price and E. A. Dudley. 

Silver oxide is prepared by adding a solution of 150 g. (0.89 mole) of silver nitrate in 300 ml. of water to a solution of 70 g. (1.75 moles) of sodium hydroxide in 300 ml. of water. Continuous shaking during the addition ensures complete reaction and results in a brown semisolid mixture. To this mixture, contained in a 1-1. flask which is cooled in an ice bath, is added 47.5 g. (0.425 mole) of 3-thenaldehyde (p. 93) in small portions with stirring. 

The oxidation is complete in about S minutes after the last of the aldehyde has been added. The black silver suspension is removed by suction filtration (Note 1) and is washed with several portions of hot water. The cold combined filtrate and washings are acidified with concentrated hydrochloric acid, precipitating 49 g. of 3-thenoic acid, which melts at 136-137°. Concentration of the mother liquors gives another 3-4 g. of acid, making a total of 52-53 g. (95-97%). Recrystallization of this acid from water raises the melting point to 137-138°. 

This silver dissolves readily in concentrated nitric acid and may be used over and over in oxidations. 

3-Thenoic acid has been prepared in low yield by oxidation of 3-methylthiophene with potassium permanganate,2-4 dilute nitric acid, chromic acid, and hydrogen peroxide,4 and by reductive dechlorination of chloro-3-thenoic acid.4 Starting with 3-iodothiophene, which is difficult to obtain, good yields are obtained by the Grignard procedure 6 or with cuprous cyanide and potassium cyanide in a sealed tube.6 

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The rates of alkaline hydrolysis of ethyl benzoate, ethyl 2-thenoate, and 3-thenoate are very similar. Also, the acid constants of benzoic acid (pAfl = 4.20) and 3-thenoic acid (pKa " 4.08) are of the same magnitude, whereas 2-thenoic acid (piCa = 3.49) is stronger. 

Furthermore, in an extension of this study, the synthesis of a phenyl-thiophene (type II) containing four ortho substituted groups has been carried out 40), (41). To resolve a -linked phenylthiophene there was chosen a compound which met all the steric requirements in order that the proposed structure be capable of existing in enanthiomorphic forms. All these requirements seem to be met by 2,5-dimethyl-4-(6 -methyl-2 -nitrophenyl)-3-thenoic acid ... 

I. The Synthesis and Resolution of 2-(6-Methyl-2-Nitrophenyl)-3-thenoic Acid. J. org. Chemistry 16, 1864 (1951). 

Tetraphenylarsonium chloride HYDROCHLORIDE, 30, 95 Tetraphenylethylene, 31, 104 2,2,3,3-Tetraphenylpropionitrile from diphenylacetonitrile and benzhydryl chloride, 39, 74 Tetra-K-propyltin, 36, 88 3-Thenaldehyde, 33, 93 3-Thenoic acid, 33, 94 3-Thenyl bromide, 33, 93, 96 7-Thiabicyclo(4.1.0)heptane, 32, 39 Thiobenzoic acid, 31,101 Thiobenzophenone, 35, 97 Thiocarbonyl perchloride, 32, 69 Thioether, preparation of dithiane,... 

ArCHO— ArCO-iH. For oxidation of 3-thenaldehyde to 3-thenoic acid, Campaigne and LeSuef mixed solutions of silver nitrate and excess alkali to... 

Thiophenecarboxyiic acid 3-Thenoic acid C5H4O2S 88-13-1 128.160 138 SH2O... 

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