4- semicarbazide

To decompose the semicarbazone it is gently warmed with concentrated hydrochloric acid (8 c.c. for each 10 g. of material) until dissolution is just complete. On cooling the solution semicarbazide hydrochloride sets to a thick crystalline mass which is filtered dry at the pump and washed, first with a little cold hydrochloric acid (1 1), then twice with 3 to 5 c.c. portions of ice-cold alcohol. The salt is dried in a desiccator. Yield 22-25 g. 

In order to obtain the free semicarbazide, 5-5 g. of the hydrochloride are ground in a small mortar with 4-5 g. of anhydrous sodium acetate (see p. 127). The paste produced by the formation of free acetic acid is transferred with a spatula to a 100 c.c. conical flask the last portions are washed in with absolute alcohol and the contents of the flask are then boiled on the water bath with (altogether) 50 c.c. of absolute alcohol. During the boiling the flask is frequently 

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Aldehydes and ketones may frequently be identified by their semicarbazones, obtained by direct condensation with semicarbazide (or amino-urea), NH,NHCONH a compound which is a monacidic base and usually available as its monohydrochloride, NHjCONHNH, HCl. Semicarbazones are particularly useful for identification of con jounds (such as acetophenone) of which the oxime is too soluble to be readily isolated and the phenylhydrazone is unstable moreover, the high nitrogen content of semicarbazones enables very small quantities to be accurately analysed and so identified. The general conditions for the formation of semicarbazones are very similar to those for oximes and phenylhydrazones (pp. 93, 229) the free base must of course be liberated from its salts by the addition of sodium acetate. 

Required Semicarbazide hydrochloride, i g. anhydrous sodium acetate, 0-9 g. acetophenone, i ml. 

Add first I g. of powdered semicarbazide hydrochloride and then 0 9 g. of anhydrous sodium acetate (or 1-25 g. of the crystalline acetate) to 5 ml. of water, and warm gently until a clear solution is obtained. Then add a solution of i ml. (i g.) of acetophenone in 5 ml. of rectified spirit, and warm the mixed solutions gently on a water-bath for... 

Form phenylhydra2ones, 2,4-dinitrophenylhydra20nes and semicarbazides. (Many oximes are too soluble for ready isolation.)... 

A) Semicarbazones. Prepared according to the directions given for acetophenone semicarbazone (p. 258), but use twice the amount of semicarbazide hydrochloride and sodium acetate. (M.ps., p. 549.)... 

Semicarbazones. Dissolve 1 g. of semicarbazide hydrochloride and 1 5g. of crystallised sodium acetate in 8-10 ml. of water add 0 - 5-1 g. of the aldehyde or ketone and shake. If the mixture is turbid, add alcohol (acetone-free) or water until a clear solution is obtained shake the mixture for a few minutes and allow to stand. Usually the semicarbazone crystallises from the cold solution on standing, the time varying from a few minutes to several hours. The reaction may be accelerated,... 

When semicarbazide Ls heated in the absence of a carbonyl compound for long periods, condensation to blurea, NHjCONHNHCONHj, m.p. 247-250 (decomp.), may result occasionally this substance may be produced in the normal preparation of a semicarbazone that forms slowly. Biurea is sparingly soluble in alcohol and soluble in hot water, whereas semicarbazones with melting points in the same range are insoluble in water this enables it to be readily distinguished from a semicarbazone. 

Dissolve 7 g. of pure oleic acid in 30 ml. of dry ethyl chloride (chloroform may be used but is less satisfactory), and ozonise at about —30°. Remove the solvent under reduced pressure, dissolve the residue in 50 ml. of dry methyl alcohol and hydrogenate as for adipic dialdehyde in the presence of 0 5 g. of palladium - calcium carbonate. Warm the resulting solution for 30 minutes with a slight excess of semicarbazide acetate and pour into water. Collect the precipitated semicarbazones and dry the... 

Hydrazine sulphate reacts with sodium cyanate in the presence of sodium carbonate to give semicarbazide, which remains in solution ... 

To isolate the semicarbazide hydrochloride, the filtered reaction mixture Is treated with excess of acetone and the resulting acetone semicarbazone is decomposed with concentrated hydrochloric acid. 

To decompose the acetone semicarbazone, warm 58 g. with 50 ml. of concentrated hydrochloric acid until it just dissolves. Cool in ice the semicarbazide hydrochloride separates as a thick crystaUine mass. Filter at the pump through a sintered glass funnel, and wash with a small quantity of alcohol and then with ether dry in the air. The yield of pure semicarbazide hydrochloride, m.p. 173° (decomp.), is 35 g. A further quantity of product may be obtained either by saturating the mother liquor with hydrogen chloride or by treating it with twice its volume of alcohol and then with ether. 

Oximes, hydrazines and semicarbazones. The hydrolysis products of these compounds, t.e., aldehydes and ketones, may be sensitive to alkali (this is particularly so for aldehydes) it is best, therefore, to conduct the hydrolysis with strong mineral acid. After hydrolysis the aldehyde or ketone may be isolated by distillation with steam, extraction with ether or, if a solid, by filtration, and then identified. The acid solution may be examined for hydroxylamine or hydrazine or semicarbazide substituted hydrazines of the aromatic series are precipitated as oils or solids upon the addition of alkali. 

Selenotriazines (Scheme 76) can be obtained starting from seleno-semicarbazide (76). 

Acetaldehyde can be isolated and identified by the characteristic melting points of the crystalline compounds formed with hydrazines, semicarbazides, etc these derivatives of aldehydes can be separated by paper and column chromatography (104,113). Acetaldehyde has been separated quantitatively from other carbonyl compounds on an ion-exchange resin in the bisulfite form the aldehyde is then eluted from the column with a solution of sodium chloride (114). In larger quantities, acetaldehyde may be isolated by passing the vapor into ether, then saturating with dry ammonia acetaldehyde—ammonia crystallizes from the solution. Reactions with bisulfite, hydrazines, oximes, semicarb azides, and 5,5-dimethyl-1,3-cyclohexanedione [126-81 -8] (dimedone) have also been used to isolate acetaldehyde from various solutions. 

All the sulfonic acid hydrazides are made from hydrazine or semicarbazide and the appropriate sulfonyl chloride in the presence of an HCl acceptor such as ammonia. 

There is a drive to develop insensitive or less sensitive munitions, ie, those less likely to accidental or sympathetic detonation. A leading candidate is 3-nitro-l,2,4-triazolin-5-one [930-33-6] (59), made by the reaction of semicarbazide and formic acid to give l,2,4-triazolin-5-one [932-64-9] foUowed by nitration of the triazolone (218). 

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). 

NitrofuraZone. 2-[5-Nitro-2-furanyl)methylene]hydrazinecarboximide, the first nitrofiiran to be employed clinically, is prepared from 5-nitro-2-furancarboxaldehyde and semicarbazide (19). This product has seen clinical use topically as an antibacterial, for systemic appHcation for bacterial infections in poultry and swine, and also has been employed as a food additive. In rats, nitrofurazone is hydroxylated at the 4 position of the furan moiety (27). The involvement of nitrenium ions has also been postulated in the mechanism of action of nitrofurazone (38). 

Cyclohexanone shows most of the typical reactions of aUphatic ketones. It reacts with hydroxjiamine, phenyUiydrazine, semicarbazide, Grignard reagents, hydrogen cyanide, sodium bisulfite, etc, to form the usual addition products, and it undergoes the various condensation reactions that are typical of ketones having cx-methylene groups. Reduction converts cyclohexanone to cyclohexanol or cyclohexane, and oxidation with nitric acid converts cyclohexanone almost quantitatively to adipic acid. 

Pyridazine aldehydes and ketones with the carbonyl group at the ring or in a side chain react in the usual manner. They form hydrazones, semicarbazides, oximes, etc. Side-chain aldehydes can be easily oxidized to pyridazinecarboxylic acids with silver nitrate and side-chain ketones are oxidized to carboxylic acids by treatment with potassium permanganate or hydrogen peroxide. 

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