Structures of sterically hindered p-hydroxystyrylpyridines and acid-base transformations of their quaternary salts

The structures of p-hydroxystyrylpyridines and a number of their new quaternary salts were studied by means of electronic absorption spectra. The reverse transformation of the salts to the corresponding quinonoid compounds was examined as a function of the pH of the medium, and the equilibrium constants were determined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1087–1091, August, 1972.     

High-pressure transesterification of sterically hindered esters

A mild, rapid, and efficient method for the solvolysis of sterically hindered esters under high pressure is described. Transesterification is carried out in the presence of DBU at room temperature and at a pressure of 10 kbar to give quantitative conversions within short reaction times. The substrates examined included aromatic and aliphatic esters of sterically hindered alcohols and phenols. An optically pure benzyl ester of phenylalanine was chosen to study racemization of the amino acid esters under high-pressure reaction conditions.     

Self-addition of a sterically hindered alkynylselenolate

[structure: see text] The unprecedented formation of a complex macrocyclic selenium-carbon ring system, which is initiated by the action of coordinating reagents upon a sterically hindered alkynylselenolate, has been observed. The crystal structure of the product could be obtained and shows a rigid tricyclic arrangement consisting only of selenium and sp(2)-hybridized carbon atoms. This reactivity stands in contrast to the corresponding unsubstituted alkynylselenolates and is an example where a bulky substituent destabilizes an adjacent unsaturated pi-system.     

Photoisomerization of sterically hindered polymethine dyes

Conclusions In sterically hindered polymethine dyes the photoisomerization process, with the formation of sterically hindered trans and di-cis forms, successfully competes with the nonradiative degradation of the energy on the higher vibrational sublevels of the ground state.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1926–1930, August, 1977.     

Claisen rearrangement of sterically hindered N-alkenylindolines

Conclusions Claisen rearrangement of N-(1-methyl-2-butenyl)-2-methyl-2-ethylindoline occurs under mild conditions upon treatment with acids at 20°C. Tricyclic compounds, namely, 6,6-dimethylperhydroeyclopent[g]-2-methyl-2-ethylindoline and 8-methyl-8-ethylpyrrolidino[h, i]-3-methyl-2-ethylindole, were obtained from 7-(1-methyl-2-butenyl)-2-methyl-2-ethylindoline.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 613–618, March, 1987.     

Aquametric microdetermination of sterically hindered ketones

Conclusions The previously developed aquametric micromethod for determining carbonyl compounds also gives reliable results when most of the sterically hindered ketones studied by us are analyzed. The determination error is ±0.3%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 942–944, April, 1972.     

Synthesis of sterically hindered aromatic aldehydes

Formylation of mesitylene, durene, and m-xylene derivatives containing electron-donor and electron-acceptor substituents by dichloromethyl methyl ether was studied in the presence of TiCl₄. A series of functionally substituted sterically hindered benzaldehydes was prepared from the products of these reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1609–1615, July, 1991.     

Synthesis of sterically hindered aromatic dialdehydes

A study was carried out on the formylation of a series of aromatic compounds containing two mesitylene or durene residues [dimesityl (I), dimesitylmethane (II), 1,2-dimesitylethane (III), 1,6-dimesitylhexane (IV), dimesityl sulfide (V), 1,1-dimesitylethylene (VI), 1,1-dimesityl-1-butene (VII), and didurylmethane (VIII)] by the action of dichloromethyl methyl ether (DCM) in the presence of A1C1₃ and TiCl₄. The corresponding dialdehydes are the major products. The formylation products when the reaction is carried out in the presence of A1C1₃ in the case of (I) and (V) contain significant amounts of monoaldehydes, while partial cleavage of the substrates with the formation of products containing only one benzene ring is observed in the case of (II) and (VIII) in addition to formylation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1700–1703, July, 1991.     

Synthesis of sterically hindered benzoquinone methacrylates

Sterically hindered p- and o-benzoquinone methacrylates, viz., 2,5-di(tert-butyl)-3,6-di-oxocyclohexa-1,4-dienyl methacrylate and 2,5-di(tert-butyl)-3,4-dioxocyclohexa-1,5-dienyl methacrylate, were synthesized by O-acylation of the lithium and tetrabutylammonium salts of 3,6-di(tert-butyl)-2-hydroxy-p-benzoquinone with methacryloyl chloride. The influence of the nature of cation and solvent on regioselectivity of the acylation was studied. The o-benzoquinone derivative obtained can serve as a paramagnetic ligand in metal complexes.     

Dipole moments of halogenonitroalkanes

The empirical dependences of the values of the dipole moments of different types of halogenonitroalkanes on the o^*, _R ⁰ constants and the electronegativity of the halogens and on the ^* constants of the hydrocarbon radicals were established.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 626–628, March, 1991.     

Modification of PET with sterically hindered diols

Poly(ethylene terephthalate) was modified by incorporating bis(hydroxyethyl) tetrasubstituted terephthalates (methyl, chlorine, and bromine) as a third component in the mole ratios of 2–50% (based on dimethyl terephthalate) which resulted in random copolyesters. The presence of steric hindrance imparted additional chain rigidity to the copolymer structure, as shown by increased glass transition temperature (T_g). The effectiveness of the steric groups for conferring rigidity to the copolymer structure was CH₃ > Cl?Br. The copolyesters which contained halogen substituents showed substantial enhancement in flame retardency compared with PET.     

New functional derivatives of sterically hindered phenols

Conclusions Dimethylaminoethyl (4-hydroxy-3, 5-ditert-butylphenyl) ketone, in contrast to certain other ketones of a series of sterically hindered phenols, reacts with phenylhydrazine, potassium hydroxide, sodium cyanide, and organic magnesium compounds as a normal -aminoketone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 920–922, April, 1968.The authors thank N.M. Emanuel for his interest in this work in the process of its fulfillment.     

Reaction of sterically hindered o-benzoquinones with diazomethane

Conclusions In contrast to certain o-benzoquinones, the sterically hindered o-quinones react with CH₂N₂ both at the oxygen atoms to give cyclic ethers, and at the C=C and C=O bonds of the quinoid ring; the predominant direction of the reaction depends on the ratio of the reactants.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2360–2362, October, 1981.     

Some heterocyclic derivatives of sterically hindered phenols

Five- and six-membered heterocyclic compounds containing sterically hindered phenols as structural fragments were obtained by dipolar 1,3-eycloaddition of substituted nitrile oxides to olefins, azomethines, and acetylenes.Translated fromIzvestiva Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 426–429, February, 1996.     

ESR spectra of sterically hindered silicon-containing phenoxyls

The ESR method was used to study a series of sterically hindered silicon-containing phenoxyls — 2-trialkyl(dialkylalkoxy)silyl-4,6-di-tert-butylphenoxyls. The parameters of the ESR spectra were determined: the constants of splitting of the unpaired electron on meta-protons of the phenoxyl ring, protons of the organosilyl substituents, and magnetic silicon nuclei, as well as the spectroscopic splitting factors. The stability of the silicon-containing phenoxyls relative to one another was determined. The influence of a second Si-containing substituent in the ortho-position and an alkyl substituent in the para-position was followed on the example of 2,6-triphenylsilyl-4-tert-butylphenoxyl and the 2,6-trimethylsilyl-4-ethylphenoxyl radical. The stability of the aroxyls is determined primarily by the steric shielding of the radical site responsible for the dimerization-rearrangement reaction.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 67–72, January–February, 1992.