Sodium semicarbazone

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. 

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.)... 

The experimental procedure to be followed depends upon the products of hydrolysis. If the alcohol and aldehyde are both soluble in water, the reaction product is divided into two parts. One portion is used for the characterisation of the aldehyde by the preparation of a suitable derivative e.g., the 2 4-dinitrophenylhydrazone, semicarbazone or di-medone compound—see Sections 111,70 and 111,74). The other portion is employed for the preparation of a 3 5-dinitrobenzoate, etc. (see Section 111,27) it is advisable first to concentrate the alcohol by dis tillation or to attempt to salt out the alcohol by the addition of solid potassium carbonate. If one of the hydrolysis products is insoluble in the reaction mixture, it is separated and characterised. If both the aldehyde and the alcohol are insoluble, they are removed from the aqueous layer separation is generally most simply effected with sodium bisulphite solution (compare Section Ill,74),but fractional distillation may sometimes be employed. 

NHjCONHNHj.HCl) and 1-5 g. of crystallised sodium acetate in 10 ml. of water in a test-tube. Add 1 ml. of acetone, close the tube with a cork and shake vigorously. Allow the mixtme to stand, with occasional vigorous shaking, for 10 minutes it is advantageous to cool in ice. FUter the crystals, wash with a httle cold water, and recrystaUise from water or dilute alcohol. The m.p. of acetone semicarbazone is 187°. 

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,... 

Oximes. The method given for semicarbazones (see 2) may be employed use 1 g. of hydroxylamine hydrochloride, 2 g. of crystallised sodium acetate and 0 5 g. of the aldehyde or ketone. It is usually advisable to warm on a water bath for 10 minutes. 

Wolff - Kishner reduction of aldehydes and ketones. Upon heating the hydrazoiie or semicarbazone of an aldehyde or ketone with potassium hydroxide or with sodium ethoxide solution (sealed tube), the corresponding hydrocarbon is obtained ... 

Ketones are more stable to oxidation than aldehydes and can be purified from oxidisable impurities by refluxing with potassium permanganate until the colour persists, followed by shaking with sodium carbonate (to remove acidic impurities) and distilling. Traces of water can be removed with type 4A Linde molecular sieves. Ketones which are solids can be purified by crystallisation from alcohol, toluene, or petroleum ether, and are usually sufficiently volatile for sublimation in vacuum. Ketones can be further purified via their bisulfite, semicarbazone or oxime derivatives (vide supra). The bisulfite addition compounds are formed only by aldehydes and methyl ketones but they are readily hydrolysed in dilute acid or alkali. 

Tropinone, CgHi30N. This substance, first prepared by Willstatter, crystallises in spear-shaped needles, m.p. 41°, b.p. 219-20°/714 mm., dissolves in ordinary solvents, is a strong base and has the properties of a ketone, giving an oxime, m.p. 111°, and a semicarbazone, m.p. 212°. It is a tertiary base and the methiodide is decomposed by alkalis producing dimethylamine and dihydrobenzaldehyde. When reduced by sodium... 

Semicarbazones are used as protecting groups as a consequence of their stability to reducing agents such as potassium borohydride, sodium boro-hydride and lithium borohydride. Semicarbazones are cleaved by strong acids and by heating in acetic anhydride-pyridine. " ... 

A-Homo-5a-cholestan-4-one (3b). A solution of sodium nitrite (2 g) in water (100 ml) is added over 1 hr to a stirred solution of 3-(5 -spiro-2, 2 -dimethyloxazolidinyl)-5a-cholestane (7 4.58 g) in aqueous 10% acetic acid (800 ml), maintained at 0-5° for 3 hr and the mixture is then allowed to stand overnight. The reaction mixture is neutralized with 10% sodium hydroxide solution and the resulting white suspension is extracted with ether. The ether extracts are washed with water, dried and concentrated to give a semisolid residue which is converted to the semicarbazone by warming in methanol solution (ca. 65 ml/g) with an excess of methanolic semicarbazide-acetate solution. The precipitate of semicarbazone is recrystallized from ethanol to give a white powder mp 239-241°. A solution of hydrochloric acid (50 ml) in ethanol (450 ml) is added to the semicarbazone and the mixture is heated at reflux for 1 hr. The clear solution is diluted with water (250 ml) and the... 

For unsubstitUted or lower alkylated dioxotriazines, it is advantageous to cyclize semicarbazones by sodium ethylate in ethylene glycol as described by Chang and XJlbricht. In this reaction 6-aza-uracil is obtained in 66% yield. The procedure was used for the preparation of labeled 6-azauracil ° and later for the synthesis of a number of 6-alkyl derivatives including 6-azathymine. °... 

Cyclization of 1-ureidopyrroles 88 with a base gave (79JHC833) pyr-rolo[2,l-/][I,2,4]triazines 89. Pyrolysis of 89 (R2 = COOH) afforded 90. Compounds 88 were prepared by treating chloroacetone semicarbazone 85 with the sodium salts of diethyl oxalacetate or oxalylacetophenone 86 to give semicarbazones 87, which were converted to 88 by the action of hydrochloric acid (Scheme 22). 

Commercial cycZopropyl methyl ketone (Matlieson Company) is redistiUed through a Widmer column over 95 per cent, passes over at llO-S-lll-S /767 mm. It is quite pure since it yields a semicarbazone, m.p. 117° the m.p. is unaffected by recrystallisation from aqueous alcohol. The ketone may be prepared from ethylene dibromide, ethyl acetoacetate and an excess of sodium ethoxide. 

A new class of cyclic dipeptidyl ureas, namely 3-hydroxy-6-oxo[l,2,4]triazin-l-yl-alaninamides 12, have been synthesized using the Ugi reaction. This reaction involved an a-keto-acid acid 8, an isocyanide 9 and semicarbazones 10 to give the Ugi adducts 11, wich were then stirred with sodium ethoxide <06JOC4578>. 

Oxidation of one molar proportion with sodium pieriodate produces two equivalents of formic acid, in accordance with the existence of hydroxyl groups attached to four contiguous carbon atoms. This oxidation (and also that carried out with lead tetraacetate) gives an aldehyde, whose semicar-bazone has an analysis corresponding to that of the semicarbazone of an ethyl formyl-methyl-furoate (XII). By oxidation of aldehyde XII with silver oxide in alkaline solution, 2-methyl-3,4-furandicarboxylic acid (XIV) was obtained this was identical with the compound described by Alder and Rickert.20 The identity was confirmed by preparation of the respective dianilides. The acid XIV has also been prepared by the reaction between the sodium salt of ethyl acetoacetate and ethyl bromopyruvate.9... 

Nitropropane Nitrosyl fluoride Nitrosyl perchlorate Nitrourea Nitrous acid Nitryl chloride Oxalic acid See under Nitromethane chlorosulfonic acid, oleum Haloalkenes, metals, nonmetals Acetones, amines, diethyl ether, metal salts, organic materials Mercury(II) and silver salts Phosphine, phosphorus trichloride, silver nitrate, semicarbazone Ammonia, sulfur trioxide, tin(IV) bromide and iodide Furfuryl alcohol, silver, mercury, sodium chlorate, sodium chlorite, sodium hypochlorite... 

Hydrazine sulphate (52 g.) and 21 g. of anhydrous sodium carbonate are dissolved in 200 c.c. of boiling water. The solution is cooled to 50°, a solution of 35 g. of potassium cyanate in 100 c.c. of water is added, and the whole is allowed to stand over night. After small amounts of hydrazodicarbonamide, produced in the reaction H2N.CO.NH.NH2 + 0=C=NH —> H2N.CO.NH.NH.CO.NH2, have been removed by filtration, 60 c.c. of acetone are added to the solution, which is again allowed to stand, with frequent shaking, for twenty-four hours. The acetone semicarbazone which has then crystallised out is filtered dry at the pump, washed with a little water, and dried on a porous plate or in vacuo. 

For the replacement of oxygen by hydrogen in ketones and aldehydes the method of Kishner and Wolff is used as often as is that of Clemmensen. In the former method the hydrazone or semicarbazone of the carbonyl compound is heated for several hours—preferably in the presence of hydrazine hydrate—in a sealed tube or autoclave with sodium ethoxide at about 160°. The explanation of the reaction is that, under the catalytic influence of the ethoxide, the hydrazone is transformed into a diimine which then decomposes in the same way as does phenyldiimine (p. 286) ... 

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