Semi-carbazid

Diketones with Diamines—qiiinazolines 11. Diketones with NH OH—isoxazolines 12. Diketones with NH NH,—pyrazoles 13. Diketones with semi-carbazide—pyrazoles 14. Diketones with ammonia—pyrazoles 15. Carbon disulfide with ammoacetamide—thiazolone 16. Nitriles and ethylene diamines—imidazolines D D D D D A D ... 

An acetoxy group at C-21 inhibits reaction of the 20-ketone with semi-carbazide hydrochloride,but in buffered medium 20-semicarbazones can be prepared in high yield even from 17-hydroxy-21-acetoxy compounds. ... 

Semi-carbazones.—Most aldehydes react with semi-carbazide, forming... 

They are usually best obtained by dissolving the aldehyde in alcohol, and adding excess of an equimolecular mixture of semi-carbazide hydrochloride, and acetate of sodium. The mixture is allowed to stand for some time and the ssmi-carbazone then precipitated by the addition of water. Some semi-carbazones are more easily prepared by substituting free acetic acid (glacial) for the acetate of sodium. Semi-carbazones are beat recrystallis from hot methyl alcohol. 

For the identification of citronellal, the semi-carbazone is the easiest cry stalline compound to prepare. It results if an alcoholic solution of citronellal be well-shaken with a solution of semi-carbazide hydrochloride and acetate of sodium. It is purified by recrystallisation from a mixture of chloroform and petroleum ether, and then melts at 84°. It also forms a well-defined naphthocinchoninic acid, which is prepared in the same manner as the corresponding citral compound. It melts at 225°. 

It forms a semi-carbazone melting at 136° to 138°, which can be obtained as follows Ten c.c. of methyl-heptenone are dissolved in 20 c.c. of facial acetic acid, and a mixture of 10 grams of semi-carbazide hydrochloride and 15 grams of sodium acetate dissolved in 20 c.c. of water is added. After half an hour the semi-carbazone is precipitated by the addition of water, and recrystalUsed from dilute alcohol. 

Reducing the availability of GABA by blocking the synthesising enzyme GAD also promotes convulsions. This may be achieved by substrate competition (e.g. 3-mercapto propionic acid), irreversible inhibition (e.g. allylglycine) or reducing the action or availability of its co-factor pyridoxal phosphate (e.g. various hydrazides such as semi-carbazide). In fact pyridoxal phosphate deficiency has been shown to be the cause of convulsions in children. 

It has been shown by H naff (1963) that the rate of reaction of several carbonyl reagents (bisulphite, hydrazine, phenylhydrazine, semi-carbazide and hydroxylamine) with aqueous formaldehyde solutions is independent of the nature and concentration of the reagent, and is therefore determined by the rate of dehydration of methylene glycol. He obtained catalytic constants for hydrogen and hydroxide ions, and a detailed study of acid-base catalysis has been made by the same method by Bell and Evans (1966). 

Nucleophilic attack at substituted ring carbon is probably the most common reaction of 1,3,4-oxadiazoles. However, few examples have been reported of nucleophilic attack at unsubstituted carbon since such compounds (19a) are relatively uncommon. The mechanism of the well-known conversion of 2-amino-oxadiazoles (in aqueous alkali) into triazoles has been studied in the case of the reaction where (19a R = NHPh) is converted to (20). This proceeds via the anion of semi-carbazide PhNHCONHNHCHO and is initiated by hydroxide attack at C-5 <84JCS(P2)537>. A similar nucleophilic attack by hydroxide on oxadiazole (19a R = 5-pyrazolyl) was followed by cyclization to the pyrazolo-triazine (21). Hydrolytic cleavage of 2-ary 1-1,3,4-oxadiazoles to aroyl-hydrazides allows use of the former as protected hydrazides. Oxadiazole (19a R = 4-... 

Nucleophilic attack on oxadiazolinone (62b) by diamino compounds NH2(CH2) NH2 (n = 0 or 2) led to oxadiazolotriaza heterocycles (64) <91H(32)237>. Nucleophilic attack followed by ring opening occurred when oxadiazolinones (62c) were treated with amines R R NH, yielding semi-carbazide derivatives R CONHN(Ar)CONR R <82JHC823>. 

N 31.38% grn-yel ndls(from AcOH, dil pyridine or coned formic acid), mp expl ca 180° sol in AcOH si sol in w, ale, eth or benz was prepd from p-nitrosodimethylaniline semi carbazide in dil AcOH with cooling(Ref 1 2) (See also Ref 3)... 

Various grades of nitrourea (p. 85) may be used in the reduction without noticeably affecting the purity of the semi-carbazide sulfate. In order to obtain the yields given in the procedure, the nitrourea was well washed, sucked dry on the filter, and air-dried. The moist material obtained after filtration is equally good (see Note 3). Runs in which 60-70 g. of nitrourea was used gave slightly lower yields than when 50 g. was used. 

The thiazine dithiones also react with hydrazine, hydroxylamine, semi-carbazide, and thiosemicarbazide. Hydrazine gives 3-aminopyrimidine-2,4-dithiones (214) (Scheme 87) [80JCR(S)148]. Thiosemicarbazide reacts in the same way as diamines to give [l,2,4]triazolo[l,5-a]pyrimidines (215) (Scheme 88). 

R1R2C=N—N=CR1R2) are formed instead. However, semicarbazones are hy-drazone derivatives that are easily accessible by the reaction of a ketone with semi-carbazide (for the mechanism, see Table 7.2). Semicarbazones can be converted into alkanes with KOferfBu in toluene at temperatures as low as 100°C. This method provides an alternative to the Wolff-Kishner reduction when much lower than usual reduction temperatures are desirable. 

Thio pyran 3 cyclo hexane 1.3 dione cycloxidim Thio semi carbazide bisthiosemi, triazamate Thio semi carbazide (4 methyl) thiazafluron... 

Various extensions are possible (see for full details), Use of aminoguanidines, semi-carbazide, and thiosemicarbazide gives, respectively, the 3-amino-l,2,4-triazine, and the 3-one and 3-thione derivatives. Use of -keto esters and -keto cyanides gives 5-ones and 5-amino derivatives, respectively. -Hydroxy ketones afford dihydro-1,2,4-triazines. Intermediates 651 and 652 can sometimes be isolated. 

Ethylmethylketone-semicarbazone, C3Hg C N.NH.CO.NH2 mw 129.16, N32.54% leaflets (from w), sp gr tnp 143-148° 135-136° soly in w 10% miscible with ale eth. Can be prepd from ethyl methyl ketone and semi-, carbazide hydrochloride in the presence of potassium acetate... 

Seaman, C. M., and Palcic, M. M., 1992, Stereochemical course of t>ramine oxidation by semi-carbazide-sensitive amine oxidase. Biochemistry 31 6829n6841. 

Streptomycin was inactivated by reducing and oxidizing agents. The bacteriostatic-activity of this antibiotic for Escherichia coli was reduced in the presence of cysteine, sodium thioglycolate, stannous chloride, sodium bisulfite, sodium hydrosulfide, sodium formate and sodium thiosulfate. Cysteine was the most active. Denkelwater, Cook and Tishler found that the cysteine inactivation of streptomycin could be reversed by iodine presumably cystine was formed during this process. Rake and Donovick inactivated streptomycin with semi-carbazide hydrochloride in order to test the sterility of concentrated streptomycin solutions. The inactivation of streptomycin by compounds containing sulfhydryl groups has been discussed by Cavallito. ... 

Semi-carbazid.—When guanidine is nitrated, by means of a mixture of nitric and sulphuric acids, a nitro guanidine is obtained, which, on reduction, yields amino guanidine, and this, on boiling with dilute acids or alkalies, yields a compound known as semi-carbazid. This in turn breaks down into ammonia, hydrazine (di-amine) and water. 

Semi-carbazid is an important reagent forming derivatives with aldehydes and ketones. Its name indicates that it is a hydrazine derivative of carbonic acid or of carbamic acid. It is also amino urea. 

The tendency of compounds RCN3=X to cyclize depends on the nature of X. When it is oxygen only open chain compounds are detected , and similarly for hydrazidic acids, RCNg=NNHAr, attempts to synthesize the cyclic form were failures . The latter type of compounds rearranged on treatment with acid to form semi-carbazides with retention of configuration. Guanyl azides can be isolated in open chain forms that cyclize on heating (reaction 94). 

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