Reaction with semicarbazide

Reactions with Amines and Amides. Hydroxybenzaldehydes undergo the normal reactions with aUphatic and aromatic primary amines to form imines and Schiff bases reaction with hydroxylamine gives an oxime, reaction with hydrazines gives hydrazones, and reactions with semicarbazide give semicarbazones. The reaction of 4-hydroxybenzaldehyde with hydroxylamine hydrochloride is a convenient method for the preparation of 4-cyanophenol (52,53). 

Methylcyclopentane-1,3,5-tnone, reaction with semicarbazide hydrochloride, 47, 84... 

Another fresh-water method which holds some promise for seawater analysis is twin cell potential sweep voltammetry, as proposed Afghan et al. [138]. In this method, semicarbazones are formed by reaction with semicarbazide... 

It is also possible to protect the carbonyl moiety of a phenacyl bromide via the reaction with semicarbazide hydrochloride then the semicarbazone can be electrolyt-ically dimerized, ultimately to afford a 2,5-diarylfuran [86]. Alternatively, the elec-trolytically formed dimer can be converted... 

Reaction with semicarbazide hydrochloride. Many simple quinones yield crystalline mono-semicarbazones by the following procedure. Dissolve 0.2 g of semicarbazide hydrochloride in a little water, add 0.2 g of the quinone and warm. The mono-semicarbazone is immediately formed as a yellow precipitate. Filter and recrystallise from hot water any bis-semicarbazone will remain undissolved. 

The formation of alternative heterocycles can be the main reaction with semicarbazides or thiosemicarbazides which are used extensively in the preparations of triazolinones and triazolinethiones. Aminoguanidines can give rise to isomeric triazoles. The preferred formation of thiadiazole (157) from the 1-acylthiosemicarbazide (Scheme 66) is explained by the protonation of N-4 in strong acid with accompanying loss of nucleophilicity, while in the presence of base its nucleophilic character is enhanced 73JOC3947) and (158) is obtained. 

By protecting the carbonyl group of a phenacyl bromide through reaction with semicarbazide hydrochloride, by reducing the resultant semicarbazone at mercury in DMF containing lithium perchlorate to obtain a dimer, and by hydrolyzing the electro-lytically formed dimer, one can synthesize a variety of 2,5-diarylfurans in excellent yield [234], In addition, Barba and coworkers [235] demonstrated that reductive dimerization of the semicarbazone derivative of phenacyl bromide... 

Fig. 6 Metabolism of compound 12 to a a-ketolactam metabolite, which can be trapped as the corresponding semicarbazone derivative by reaction with semicarbazide...

To carry out the detection of cyanates, the formation of a blue-violet precipitate formed with a solution of curpic salt in pyridine (3) or the specific reaction with semicarbazide hydrochloride giving rise to hydrazodicarbon-amide NH2CONHNHCONH2 (4) may be employed. 

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