94420-70-9Relevant academic research and scientific papers
Semiquantitative Determination of Quinonoid Structures in Isolated Lignins by 31P Nuclear Magnetic Resonance
Argyropoulos, Dimitris S.,Zhang, Liming
, p. 4628 - 4634 (1998)
A semiquantitative analytical method has been developed for the determination of the total quinonoid content (o-benzoquinones and p-benzoquinones) of soluble lignins. The method is based on detailed measurements and observations made with model o- and p-quinones, which in dry organic solvents were shown to form adducts with trimethyl phosphite in quantitative yield. These adducts gave 31P NMR signals for o- and p-quinones at around -46 and -2 ppm, respectively. In the presence of moisture and lignin the adducts from o-quinones were shown to be hydrolyzed to the open ring product, dimethylphenyl phosphate (-2 ppm), at an overall yield of ～70%. Similarly, the hydrolysis yields of p-quinone adducts with trimethyl phosphite were ～70%. Consequently, a number of important issues in relation to the use of trimethyl phosphite toward the quantitative analysis of quinonoid groups in lignins have been investigated, which permitted the development of an experimental semiquantitative protocol recommended for spectral acquisition.
Preparation of Regioselectively Protected Hydroquinones by Phosphorylation of p-Benzoquinones with Trialkyl Phosphites
Duthaler, Rudolf O.,Lyle, Paulette A.,Heuberger, Christoph
, p. 1406 - 1426 (2007/10/02)
The title reaction has been applied to 10 monosubstituted p-benzoquinones (Scheme 2, Table).The regioselectivity of the O-phosphorylation is influenced by bulky substituents (t-butyl and trimethylsilyl) and, electronically, by the methoxy group.The regioselectivity, which is high in nonpolar media (benzene), is lower in polar solvents (CH2Cl2 and CH3CN).The synthetic potential of this transformation, exemplified by the preparation of compounds 29 (Scheme 3) and 32 (Scheme 4), is considerably extended by applying milder methods for the phosphate hydrolysis and by using the reagent couple P(OCH3)3/trimethylsilyl chloride, which gives clean access to p-hydroxyphenyl phosphates. p-Benzoquinones 4h and 4i with strong ?-acceptor substituents react in a different way, giving phosphonates.The electronically induced regioselectivity of the O- and C-phosphorylation is in accordance with the preferences expected for the attack by a nucleophilic phosphorylation agent.
