Carboxylic acids with potassium hydroxide

Salicylic acid can be prepared by the oxidation of o-hydroxy-benzyl alcohol, by the fusion of o-toluenesulphonic acid and other ortho acids with potassium hydroxide, by heating with water the diazo compound formed from anthranilic acid. It can be obtained with a favorable yield when o-cresol is fused with potassium hydroxide and lead peroxide the latter compound oxidizes the methyl radical to carboxyl. A mixture of o- and p-hydroxybenzoic acid is obtained from phenol by the Tiemann-Reimer synthesis (507). 

Crude oils contain carboxylic acids. These are analyzed by titration with potassium hydroxide and the result of the analysis is expressed in mg of KOH/g crude. 

The most widely used method for the preparation of carboxylic acids is ester hydrolysis. The esters are generally prepared by heterocyclization (cf. Chapter II), the most useful and versatile of which is the Hantzsch s synthesis, that is the condensation of an halogenated a- or /3 keto ester with a thioamide (1-20). For example ethyl 4-thiazole carboxylate (3) was prepared by Jones et al. from ethyl a-bromoacetoacetate (1) and thioformamide (2) (1). Hydrolysis of the ester with potassium hydroxide gave the corresponding acid (4) after acidification (Scheme 1). 

Rauwolscine gives colour reactions like those of yohimbine and the absorption curves of the hydrochlorides of the two alkaloids are very similar. Heated to 300°/5 mm. rauwolscinic acid forms barman (p. 490) and 3-ethylindole and on fusion with potassium hydroxide decomposes into indole-2-carboxylic acid, isophthalic acid, barman and an unidentified indole derivative. Rauwolscine itself on distillation with zinc dust produces barman, 2-methylindole (scatole) and tsoquinoline. It is suggested that the alkaloid has the skeletal strueture suggested by Seholz (formula XIV, p. 508) for yohimbine, the positions of the hydroxyl and earbomethoxy grouf s being still imdetermined. 

Double dehydrobromination of cis- and tranj-l-(bromodifluoromethyl)-2-bromocyclohexane with potassium hydroxide gives, as the final product, 1 -cyclohexene-1-carboxylic acid as a result of the hydrolysis of the intermediate, 1-cyclohexenecarbonyl fluoride 4 (equation 4)... 

A cursory inspection of key intermediate 8 (see Scheme 1) reveals that it possesses both vicinal and remote stereochemical relationships. To cope with the stereochemical challenge posed by this intermediate and to enhance overall efficiency, a convergent approach featuring the union of optically active intermediates 18 and 19 was adopted. Scheme 5a illustrates the synthesis of intermediate 18. Thus, oxidative cleavage of the trisubstituted olefin of (/ )-citronellic acid benzyl ester (28) with ozone, followed by oxidative workup with Jones reagent, affords a carboxylic acid which can be oxidatively decarboxylated to 29 with lead tetraacetate and copper(n) acetate. Saponification of the benzyl ester in 29 with potassium hydroxide provides an unsaturated carboxylic acid which undergoes smooth conversion to trans iodolactone 30 on treatment with iodine in acetonitrile at -15 °C (89% yield from 29).24 The diastereoselectivity of the thermodynamically controlled iodolacto-nization reaction is approximately 20 1 in favor of the more stable trans iodolactone 30. 

Subsequently it was found140 that ethyl 2-alkyl-1//-azepine-1-carboxylates can be isolated from a mixture of isomeric 1//-azepines by stirring the mixture with potassium hydroxide in ethanol at room temperature. Apparently, this method, which is limited to 2-alkylated azepines, depends on the slower rate of hydrolysis (and subsequent decomposition of the resulting 1H-azepine-l-carboxylic acid) of the sterically hindered 1-(ethoxycarbonyl) group. Although the yields of l//-azepines are poor (4-7%, vide supra), the method provides access to otherwise difficult to obtain, isomerically pure 2-alkyl-1//-azepines. Under the basic hydrolysis conditions aryl 2-alkyl-l//-azepine-1-carboxylates undergo transesterification to the l-(ethoxycarbonyl) derivatives. 

CN 7-chloro-2,3-dihydro-2-oxo-5-phenyl-lH-l, 4-benzodiazepine-3-carboxylic acid monopotassium salt compd. with potassium hydroxide... 

Refluxing of 9-fluorenone-l-carboxylic acid with zinc dust and copper sulfate in aqueous potassium hydroxide for 2.5 hours afforded 9-fluorenol-1-carboxylic acid in 94% yield [1004]. Reduction with sodium borohydride in aqueous methanol at 0-25° converted 5-ketopiperidine-2-carboxylic acid to /ra j-5-hydroxypiperidine-2-carboxylic acid in 54-61% yield [1005], On the other hand, reduction of V-benzyloxycarbonyl-5-ketopiperidine-2-carboxylic acid gave 89% yield of V-benzyloxycarbonyl-cis-5-hydroxypiperidine-2-car-boxylic acid under the same conditions [1005],... 

Heating 1,2,4-benzotriazines (128) with bases gives aniline, nitrogen and a carboxylic acid (60G1H3). 2-Substituted l,2,4-benzotriazin-3-ones (116) with potassium hydroxide in... 

The cadmium secocorrinoid carboxylic acid (102 M = Cd) also undergoes photocyclization to the acid (103 M = Cd), which on transmetallation to the nickel(II) complex (103 M = Ni) and treatment with triethylamine and acetic acid yields the parent corrin complex (100 M = Ni).268 The decarboxylation process is extremely facile. A related base-catalyzed cyclization of the secocorrinoid aldehyde (104) gives the corrin complex (105), which can be decarbonylated to the parent complex (100 M = Ni) by treatment with potassium hydroxide (Scheme 66).268... 

The loss of a bromide ion when situated in a -position to a carboxylate group occurs very readily under mildly basic conditions. Thus in an alternative synthesis of phenylacetylene (Expt 5.24), cinnamic acid dibromide is converted into /1-bromostyrene under the influence of hot aqueous sodium carbonate solution. Dehydrobromination to yield the acetylenic compound is then achieved in the usual manner with potassium hydroxide. 

The reaction of a carboxylic acid with diazomethane is mild and efficient Diazomethane is usually prepared by reaction of potassium hydroxide with N-methyl-A/-nitroso-p-toluenesulfonamide (HAZARD carcinogenic) and used in ether solution since it is volatile, toxic, and explosive.44 Therefore, the method is most suitable for small scale reactions. A useful feature of the reaction is that diazomethane is intensely yellow and the consumption of the reagent is easily detected by the disappearance of the colour. It may be convenient to prepare the diazomethane in situ 45 (Trimethylsilyl)diazomethane is a safer alternative to diazomethane for the preparation of methyl esters and it is commercially available as a 2.0 M solution in hexanes,46 47... 

From Hexa-chlor Ethane.—It may also be prepared by oxidizing a derivative of ethane, viz., hexa-chlor ethane, CCle, with potassium hydroxide. This reaction may be considered as yielding the complete oxidation product of ethane by the replacement of the six chlorine atoms by six hydroxyl groups. This then loses water, as in the case of all compounds which contain more than one hydroxyl group linked to one carbon atom, and di-carboxyl, or oxalic acid results, as follows. 

With the simple aryl halides such as the mono-chlor derivatives of benzene or its homologues this reaction does not take place. Tf, however, a benzene halide has also substituted in the ring two nitro, sul-phonic acid or carboxyl groups, in the ortho and para positions to the halogen, then treatment of the halide with potassium hydroxide results in replacing the halogen with hydroxyl and the corresponding substituted phenol will be obtained. 

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