2.6- Di-tert-butyl-p-benzoquinone

A cobalt complex salcomine (7.39) oxidizes substituted phenols but unsubstituted at para position, such as 2,6-di-fert-butylphenol (7.40), to give the corresponding p-quinone, 2,6-di- tert-butyl-p-benzoquinone (7.41). 

On controlled current electrolysis (200 mA), 2,6-di(terf-butyl)-p-cresol (69) underwent nucleophilic hydroxylation, methoxylation or acetoxylation depending on the solvent system used (IM H2O, MeOH or 0.2 M NaOAc-AcOH in MeCN) to afford the corresponding cyclohexa-2,5-dienones 70, 71 and 72 in 86, 88 and 91% yields, respectively. In the case of 2,4,6-tri(tert-butyl)phenol (73), 2,6-di(tert-butyl)-p-benzoquinone (74) was produced in 96% yield through cyclohexa-2,5-dienone 75 , as shown in Scheme 13. 

Burman and Albertsson [116] have developed methods for quantifying certain theoretical degradation products of Irganox 1010 and Irgafos 168 from pharmaceutical solutions consisting of 10% ethanol in water. The degradation products of Irganox 1010 were 2,4-di-tert-butylphenol, 2,6-di-tert-butyl-p-benzoquinone, 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid, 2,6-... 

Oxidation of 2,6-di(tert-butyl)phenol (23) provides a useful test for comparing the activity of various catalysts 23 is oxidized with O2 catalyzed by metal-amine complexes to give only two products, 2,6-di(terr-butyl)-p-benzoquinone (74) and 3,3, 5,5 -tetra(ferf-butyl)diphenoquinone (24) (Scheme 46). Of the cobalt catalysts 230, 231, 232 and 237, the use of Co(salN-Medpt) in MeCN (room temp., 1 h) provided the most effective results, in which 74 was obtained in 100% yield. The oxidation rate and yield were dependent on... 

Stabilization of the polymeric and monomeric components is required to avoid premature radical polymer formation of UP resin dissolved in styrene by heat, light, or metallic initiators. Insufficient stabilization causes an increase in viscosity that makes further processing impossible. Quinones and phenols in concentrations < 500 ppm are proven stabilizers for unsaturated polyester. The most important examples are hydroquinone, p-benzoquinone, tert-butyl-brenzcatechol and 2,6-di-tert-butyl-p-cresol [574]. For styrene, stabilization with 25 ppm p-tert-butyl-brenz-catechol is required [575]. Slight yellowing caused by the stabilizers is possible appropriate brighteners are recommended for optically demanding applications. 

In COj-expanded CH Cl (62 bar, 70°C), 2,6-di-tert-butyl-l,4-benzoquinone was obtained in a yield of 97% [113b]. p-Substituted phenols, for example, syiingyl alcohol, could be oxidized to p-BQ in the presence of 5-coordinate Co(II)salen complexes (Scheme 14.13) [116]. 

Abbreviations Ac acetyl Bn benzyl BSP 1-benzenesulfinyl piperidine BTIB bis(trifluoroacetoxy)iodobenzene DAST (diethylamino)sulfur trifluoride DDQ 2,3-dichloro-5,6-dicyano-/)-benzoquinone DMDO dimethyldioxirane DMTSF dimethyl(methylthio)sulfonium tetrafluoroborate DMTST dimethyl(methylthio)sulfonium triflate DTBMP 2,6-Ai-tert-butyl-4-methylpyridine DTBP 2,6-di-tert-butylpyridine DTBPl 2,6-di-tert-butylpyridinium iodide FDCPT l-fluoro-2,6-dichloropyridinium triflate FTMPT l-fluoro-2,4,6-trimethylpyridinium triflate IDCP iodonium dicollidine perchlorate IDCT idonium dicollidine triflate LPTS 2,6-lutidinium p-toluenesulfonate LTMP lithium tetramethylpiperidide Me methyl MPBT S-(4-methoxyphenyl) benzenethiosulflnate NBS A-bromosuccinimide NIS A-iodosuccinimide NlSac A-iodosaccharin PPTS pyridinium p-toluenesulfonate TBPA tris(4-bromophenyl)ammoniumyl hexachloroantimonate Tf trifluoromethanesulfonyl TMTSB methyl-bis(methylthio)sulfonium hexachloroantimonate TMU tetramethylurea Tr trityl TTBP 2,4,6-tri-tert-butylpyrimidine. 

To our knowledge, the first examples of asymmetrically substituted monocyclic phosphoranes are 60 and 61, described by Moriarty et al.135 and involving the reaction of a substituted o-benzoquinone136,137 (Scheme 6) on an aminophosphine (59), itself obtained by alcoholysis of 58 with l-( — )-menthol. In contrast to the amino phosphine 53 (Scheme 5), 59 is a mixture of the diastereoisomers 59a and b, and its reaction with 3,5-di-tert-butyl-l,2-benzoquinone yields two diastereoisomeric phosphoranes, 60a and b. Finally, alcoholysis of the P(V)—NR2 bond138 in 60a and b leads to 61a and b or 62. 

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