Phenolics Bromine modification

This procedure is described by Lock 2 a modification using a small amount of phenol has been published.3 The patent literature discloses the use of a tertiary amine, such as pyridine, and its combination with other solvents for the monobromination of pyrene with elemental bromine.4 Brominating agents, such as N-bromosuccinimide5 and N-bromohydantoins,6 have also been used. 

Answer By bromination of phenol. However, since phenol is such a reactive molecule towards electrophilic substitution, the solvent used is CSa and the Lewis acid catalyst is omitted. This modification of procedure V-5 prevents polybromination of phenol. Thus the synthesis of Xl I-e becomes... 

Preussomerin I 697 and ( )-preussomerin G 698 were obtained from 620 with a five- and six-steps sequence in 15% and 12% overall yield, respectively, through modifications of substituents of the dioxocin ring. Thus, attack of lithium methoxide from the less hindered face of the enone 620, followed by protection of the phenolic oxygen as its methyl ether provided the methoxy adduct 692. The ketone 693 was obtained through a benzylic bromination-solvolysis-oxidation protocol, which required only a single purification. The C(2)-C(3) olefin was introduced by selective silylation of the C-l carbonyl of diketone 693 and oxidation of the silyl enol ether with Pd(OAc)2. Enone... 

The number of unsaturated bonds can be determined by a titration with a standard solution of bromine dissolved in glacial acetic acid. The sample is also dissolved in glacial acetic acid to which sodium and ammonium acetate are added, so as to give a final concentration of 0-5 and OT M respectively. The cathodic current of bromine is measured with a short circuit system using a rotating platinum indicator, and a calomel or chloranil reference electrode at the potential of the reference electrode. Several unsaturated open chain compounds and terpenes have been titrated in this way.( ) Other modifications of this technique have been used to determine the amount of unsaturation in fats in methanolic solutions. The standard solution of bromine is prepared in methanol, saturated with sodium bromide, and the methylester of stearic acid is added to suppress the maxima. If the methanolic solution is acidified, OT M potassium bromate with OT M sodium bromide can be used instead of bromine. The bromine generated in homogeneous solution can be used to analyse xylenol and cresol fractions of coal-tars. Other phenolic compounds may be similarly determined. The method was used for the determination of small concentrations of styrene... 

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