THE OXIDATION OF PHENOLS: II. THE OXIDATION OF 2,4-DI-t-BUTYLPHENOL WITH PEROXY RADICALS

Abstract

Ten p r o d~~c t s f r o m the osidatior~ of 2,4-di-t-butylpher~ol wit11 L-butyl perosy radicals have been identilied. They can be subdivided into three groups, depending on the type of radicalradical coupling reaction by which they are prod~rced or iri which their precursors are forn~ed:(i) pher~oxy-perosy coupling, ( i i ) phenoxjr-phenoxy coupling a t the 6 positior~s, and (iii) phenoxy-phenoxy couplir~g through the oxygen atoll1 of one radical and the 6 positio!~ of the second radical. Products resulting from still other phenosy-phenoxy coupling reactions are undoubtedly formed in 111i11or amounts.The products from the oxidation of 2,4-di-t-butylphenol xrith t-butyl peroxy radicals have been studied as a part of our general investigation into the oxidation of phenols (I). This compound was chosen as a representative 2,1-dialliyl phenol which might be expected to give a simpler mixture of products than a phenol containing a inethyl group, since products coupled through the methyl group (such as dihydroxy bibenzyls and stilbenequinones) would not be formed. In spite of this siinplification 110 less than 10 products were identified, and the thin-layer chromatographic (t.1.c.) plates showed t h a t many others were present. T h e products were separated by coluilln chroillatography on silica ( I ) . Their relative yields depended not only on the exact conditions of the reaction but also on the speed 11-ith nrhich they were separated. The latter variation is due to the fact that inany of the initial products are unstable peroxides which decoinpose on exposure to light and heat and even t o the inildly acidic silica column itself.By analogy with 2,G-dialliyl phenols (I) we inay expect to get products resulting from phenoxy-peroxy and phenoxy-phenoxy radical coupling reactions. Elowever, in the present case, the existence of a hydrogen atom in the 6 positioil leads to products of increased complex it^^ because of the rapid rearrangement of those intermediates \\ ith an o-quinolide structure. For convenience, the overall reaction is divided into three parts.Firstly, combination of the initially forined phenoxy radical with a t-but11 peroxy radical.3,s-Di-t-butyl-o-benzoquinone (11) was one of the major products (-10yo), but its probable precursor (I) \vas not identified. The conversion of I into I1 inay occur either directly (cf. ref. 1) or after rearrangement to an o-peroxy phenol. The 4-peroxy-cyclohexadienone, 111, found in s-lOyO yield, is siinilar to the major products formed fro111 ,3,4,6-trialliyl phenols (1). Co~npound I11 decolnposed slo~vly on the t.1.c. plates to give 2-t-butyl-p-benzoquinone (I\[) and other unidentified products. No compound corresponding t o the addition of the peroxy radical a t the 2 position of the original phenol \\-as identified, nor was its expected decomposition product, 4-t-but)il-o-benzoquinone, detected.Secondly, colllbination of two phenoxy radicals through their carbon atoms in position 6. T h e biphenol V and its precursor mere not identified anlong the products under the s...

Phenols as Antioxidants

“…Oxidation of compounds containing a para-methyl can, under certain conditions, lead to the formation of stilbenequinones, 6, possibly by disproportionation of 3 to 5, dimer formation and continued oxidation of the dimer 32 , or more likely by formation of a quinone methide followed by dimer formation. Oxidation of phenols with a 'free' ortho position gave (unexpectedly) a complex array of at least ten products 32 , classified into three types, as shown in Scheme 2: (A) Peroxyl adduct at the free ortho site, followed by decomposition to an ortho quinone, 7 → 8 → 9; (B) carbon-carbon radical recombination at the ortho positions through 11 yielding a bis-ortho-phenol, 12, which in turn adds peroxyl to form the peroxycyclohexadienone dimer, 13; and (C) phenoxyl radical self-addition at the ortho position followed by the reaction sequence 14 → 15 → 16, the latter being the isolated product 33 .…”

Absolute rate constants for hydrocarbon autoxidation. V. The hydroperoxy radical in chain propagation and termination

“…method for the quantitative estimation of I formed in BMPinhibited oxidations has recently been developed in these laboratories (16,17). I n a 1:1 hexane:benzene solvent mixture the 4-hydroperoxy derivative Ia (I with R = H , synthesized b y the method of Kharasch and Joshi (18)) was well resolved from faster running organic I (e.g.…”

“…I n a 1:1 hexane:benzene solvent mixture the 4-hydroperoxy derivative Ia (I with R = H , synthesized b y the method of Kharasch and Joshi (18)) was well resolved from faster running organic I (e.g. the isobutyronitrile derivative, R = (CH3)2C(CN), which might also be formed in the oxidation (16,17)). However, Ia was not resolved from the or,al-azo-bis-isobutyronitrile (AIBN) used to initiate oxidation.…”

Molecular Iron-Based Oxidants and Their Stoichiometric Reactions

“…In the case of the phenol oxidations, no product characterization was reported. It is however known from previous studies with oxoiron(IV) species [38] and from autooxidation studies that the oxidation of sterically hindered phenols usually yields complicated mixtures of dimerized diphenoquinones [39][40][41], e.g., as illustrated in Scheme 9.…”

“…The characterization of ferryl (Fe IV ¼O) [80][81][82][83][84][85][86] and perferryl (Fe V ¼O) [87] complexes are important steps towards the discovery of robust catalysts. Their potential strong electrophilic nature will faciliate formal O-atom transfer reactions with electron rich substrates such as sulfides and phosphines [39,84,[88][89][90][91][91][92][93]. High-valent iron species are far too unstable to be put into a bottle and so must be generated in situ, ideally using benign less reactive terminal oxidants.…”