Crystalline derivatives preparation acid chlorides

Aqueous solutions give with ferric chloride the characteristic reactions of the neutral salt of the acid (p. 348). Identify the carboxylic acids by the tests already given (Section 14, p. 347), or by the preparation of one of the crystalline derivatives below. 

From l-cyclohexyl-3-ethyldiaziridine, crystalline derivatives have been prepared with p-toluenesulfonyl chloride and with 3,5-dinitro-benzoyl chloride, e.g., 46/ The quantitative liberation of iodine from acid iodide solution characterizes these compounds as true diaziridines. 

G) Identification of Monohydroxy Compounds. The evolution of hydrogen chloride, when acetyl chloride or phosphorus trichloride is added to a compound, indicates the possible presence of a hydroxy group. For identification purposes a derivative should be prepared. 3, 5-Dinitrobenzoic acid forms crystalline derivatives with hydroxy compounds. The melting points of the esters are utilized for identification. 

Activation of Carboxylic Acids Synthesis of Acyl Imidazoles. iV,AA-Carbonyldiimidazole (1) converts carboxylic acids into the corresponding acylimidazoles (2) (eq 1). The method can be applied to a wide range of aliphatic, aromatic, and heterocyclic carboxylic acids, including some examples (such as formic acid and vitamin A acid) where acid chloride formation is difficult. The reactivity of (2) is similar to that of acid chlorides, but the former have the advantage that they are generally crystalline and easily handled. Isolation of (2) is sirr5>le, but often unnecessary further reaction with nucleophiles is usually performed in the same reaction vessel. Conversion of (2) into acid chlorides (via reaction with HCl), hydrazides, hydroxamic acids, and peroxy esters have all been described. Preparation of the more irr5)ortant carboxylic acid derivatives is described below. 

The synthesis of discotic liquid crystalline cyclohexanes is relatively straightforward. Both classes of derivative (the scylloinosi-tol ethers and esters) are synthesized from commercially available scylloinositol (Scheme 60). The esters are prepared by treatment with an excess of acid chloride in trifluoroacetic acid [222], whereas the ether is synthesized using potassium hydroxide and hexyl bromide [223]. The mesophase... 

The procedure is not usually applicable to aminosulphonic acids owing to the interaction between the amino group and the phosphorus pentachloride. If, however, the chlorosulphonic acid is prepared by diazotisation and treatment with a solution of cuprous chloride in hydrochloric acid, the crystalline chlorosulphonamide and chlorosulphonanilide may be obtained in the usual way. With some compounds, the amino group may be protected by acetylation. Sulphonic acids derived from a phenol or naphthol cannot be converted into the sulphonyl chlorides by the phosphorus pentachloride method. 

Sulfonamides (R2NSO2R ) are prepared from an amine and sulfonyl chloride in the presence of pyridine or aqueous base. The sulfonamide is one of the most stable nitrogen protective groups. Arylsulfonamides are stable to alkaline hydrolysis, and to catalytic reduction they are cleaved by Na/NH3, Na/butanol, sodium naphthalenide, or sodium anthracenide, and by refluxing in acid (48% HBr/cat. phenol). Sulfonamides of less basic amines such as pyrroles and indoles are much easier to cleave than are those of the more basic alkyl amines. In fact, sulfonamides of the less basic amines (pyrroles, indoles, and imidazoles) can be cleaved by basic hydrolysis, which is almost impossible for the alkyl amines. Because of the inherent differences between the aromatic — NH group and simple aliphatic amines, the protection of these compounds (pyrroles, indoles, and imidazoles) will be described in a separate section. One appealing proj>erty of sulfonamides is that the derivatives are more crystalline than amides or carbamates. 

Aquo-triammino-platinous salts have been described of general formula [Pt(NH3)3HsO]R2. These are prepared by passing a current of air through a solution of diammino-dihydroxylamino-platinous chloride, [Pt(NH3)2(NH2OH)2]Cl2, containing ammonia and ammonium sulphate and a small quantity of any copper salt. Oxidation takes place, and a colourless crystalline precipitate is obtained which is soluble ill warm dilute sulphuric acid. Analysis of this product indicates that it is probably a diplatinum derivative of composition... 

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