IN acetic anhydride the acidity of perchloric acid is markedly increased; the active "acidic" entity is probably the acetyl cation CH,CO+ (possibly solvated in the form (CH,CO),O+) rather than the solvated proton (which, in acetic acid, is in the form CH,COOH,+). There is considerable evidence in support of this1 t o l2Thus bases, such as amides and purines,13314$L5 too weak to be titrated successfully in acetic acid, can be titrated potentiometically in acetic anhydride by using a modified glasscalomel electrode system. This led to the investigation of the basic properties of well-known derivatives of carbonyl compounds in this solvent. Since these are often prepared in the course of research in organic chemistry, it seemed desirable to have a method of direct titration. No satisfactory method has been reported concerning the direct titration of these derivatives as bases. The method described here is similar to that used by Wimerls for titrating amides, and is applied to semicarbazones, phenylhydrazones, 4-nitrophenylhydrazones and 2,4-dinitrophenylhydrazones.
METHOD SAMPLES FOR ANALYSIS-When commercial samples are available, the: purest grades should be used without further purification, provided their melting-points agree with those quoted in reliable literature sources. Otherwise they should be purified by recrystallisation until the melting points are constant. Samples that are made should be purified likewise.
REAGENTS-Acetic anhydride and glacial acetic acid-Good quality commercial grades. Perchloric acid-72 per cent. aqueous solution, analytical-reagent grade.The titrant-Prepare a 0.2 N perchloric acid in a mixture of equal parts of acetic anhydride and glacial acetic acid.Although it may become a pale straw colour on storage it does not lose strength for at least two weeks (cf. Streulil7). Standardise it by potentiometric titration with analytical-reagent grade potassium hydrogen phthalate dissolved in glacial acetic acid, and check a t frequent intervals.
APPARATUS-Glass electrode-Cambridge wide-range type. Immersed in acetic anhydride for 12 hours before use.Modi$ed calomel electrode-Sleeve type; the aqueous solution being replaced by a 0.1 M solution of anhydrous lithium perchlorate in acetic anhydride as described by Wimer.ls Potentiometer-Cambridge pH meter, used as a potentiometer. Incorporate a Weston standard-cell into the circuit when necessary, to allow for reversed polarity of the electrodes in non-aqueous media.18 Allow to stand for a t least 12 hours before use.
6:7:8:9‐Tetrahydro‐1‐oxo‐4:5‐benzindane and its 3‘‐methoxy analogue have been synthesised from 1‐oxotetralin and 1‐oxo‐6‐methoxytetralin. Side chains typical of cortical hormones have been built up by known methods via the intermediate ethynyl alcohols: 1‐acetoxy‐1‐glycollyl‐6:7:8:9‐tetrahydro‐4:5‐benzindane has thus been produced. In the case of the corresponding methoxy analogue, ring expansion probably occurs to furnish the corresponding “homo” compound—a substituted hydrophenanthrene.
The action of basic reagents on 2‐cyano‐6‐methoxy‐2‐methyl‐1‐oxotetralin leads to ring fission and the formation of γ(2‐carboxy‐5‐methoxyphenyl)α‐methylbutyronitrile.
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