The relative chain propagation constants and the regioselectivities of the oxidations of o‐cymene and 2‐isopropyl‐1,4‐dimethylbenzene were determined by competitive oxidations of the hydrocarbons with cumene. As expected, the reactivity of the tertiary CH bond of the isopropyl group is considerably decreased by o‐methyl groups.
Also in α‐isopropylnaphthalene a considerable decrease in the reactivity of the tertiary CH bond takes place.
The decrease of the chain propagation constants effects a decrease of the oxidabilities of o‐substituted isopropyl aromatics. In the case of the methyl isopropyl benzenes the increase of the chain termination constants by primary peroxy radicals must also be taken into consideration. This results in a decrease of the oxidabilities which can be observed even in p‐cymene (in comparison with cumene).
The products of the autoxidation of phenyl cyclopropane (I), phenyl cyclobutane (II), phenyl cyclopentane (III), phenyl cyclohexane (IV), phenyl cycloheptane (V) and phenyl cyclooctane (VI) were analyzed after reduction of the reaction mixtures with LiAlH4. As products of the attack on the α‐CH bonds the corresponding 1‐phenyl cycloalkanols and 1‐phenyl alkan‐1‐ols were found. In the case of phenyl cyclopropane some SR2 ring opening probably takes place.
The oxidabilities \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm k}_{\rm p} /\sqrt {{\rm k}_{\rm t}} $\end{document}, the chain termination constants kt, the absolute chain propagation constants kp and the relative chain propagation constant (kp)rel were determined for the phenyl cycloalkanes I—VI. As it is to be expected on the basis of the I‐strain concept the autoxidation rate of phenyl cyclopentane (III) is considerably higher than that of phenyl cyclobutane (II) and phenyl cyclohexane (IV).
Chromium stearate and chromium acetylacetonate are very active catalysts both for the oxidation of hydrocarbons by molecular oxygen and for the decomposition of organic hydroperoxides. During these reactions they also catalyze the oxidation of secondary alcohols to the corresponding ketones by organic hydroperoxides. From organic hydroperoxides and chromium(III)compounds chromium (VI) compounds are formed which are probably the effective agents oxidizing secondary alcohols to ketones.
The catalytic decomposition of cumene, 1‐methylcyclohexyl and cyclohexyl hydroperoxides was studied in cyclohexane, cis‐ and trans‐1,4‐dimethylcyclohexane and cis‐pinane as the solvents. The stearates and the acetylacetonates of manganese, cobalt and chromium, the acetylacetonates of molybdenum and vanadium, n‐butyl orthoborate and n‐butyl metaborate were used as the catalysts. The chromium‐, vanadium‐, molybdenum‐ and boron‐containing catalysts brought about some Hock‐type decomposition of cumene hydroperoxide and thus proved to be acidic. Of these more of less acidic catalysts only molybdenyl acetylacetonate effected a partially stereospecific hydroxylation of the tertiary CH‐bonds in cis‐ and trans‐1,4‐dimethylcyclohexane. The well‐known selectivity of chromium catalysts for the ketone formation during the decomposition of secondary hydroperoxides is caused by the catalytic oxidatio of secondary alcohols by hydroperoxides in the presence of chromium compounds.
In the presence of all the catalysts used the free‐radical pathways of the hydroperoxide decomposition predominated, and the attack of the intermediate radicals on the starting hydroperoxide was more important than the attack on the solvent molecules.
Carrageenan extracted from Eucheuma cotionii and Chondrus crispus contained small but significant concentrations of nitrogen. Analysis of the nitrogen content by the Lowry and Coomassie Blue protein methods indicated that the nitrogen was largely proteinaceous in nature and not bound ammonia. Treatment of extracted carrageenans with proteases suggested that a portion of the nitrogen could be removed by enzymatic hydrolysis. Nitrogen losses resulted in changes in Carrageenan solution properties which were similar in pattern to those observed during commercial alkaline modification of carrageenan. These results indicated that the presence of bound protein may be an important determinant in the reactivity and properties of carrageenan.
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