Synthesis and thermal properties of azo-peroxyesters

Abstract  New azo-perester derivatives of tert-butyl and tert-amyl hydroperoxides were obtained in reactions of azo acid chlorides with hydroperoxides in the presence of an inorganic base. Obtained azo-peresters possess two kinds of the labile functional groups: the azo group and also the perester group. The data from DSC experiments indicate that in the case of azo-perester derivatives of tert-amyl hydroperoxide, the perester group decomposes at a somewhat lower temperature than in the case of tert-butyl derivatives, whereas azo groups decompose at somewhat higher temperature in the case of derivatives with tert-amyl substituent. Graphical abstract        

Synthesis and thermal properties of asymmetrical azo-peresters

Abstract  

New asymmetrical azo-perester derivatives of tert-butyl and tert-amyl hydroperoxides were obtained by reacting azo acids with hydroperoxides in the presence of N,N′-carbonyldiimidazole. The obtained azo-peresters possess two labile functional groups: the azo group and the perester group. Data from dynamic differential scanning calorimetry (DSC) experiments indicate that the azo groups decompose at somewhat lower temperatures than the perester groups.     

Excess Enthalpies of (2,2,4-Trimethylpentane or Cyclohexane) + Methyl tert-Butyl Ether + tert-Amyl Methyl Ether at 25°C

Microcalormetric measurements of excess molar enthalpies at 25°C are reported for two ternary mixtures 2,2,4-trimethylpentane + methyltert-butyl ether +tert-amyl methyl ether and cyclohexane + methyltert-butyl ether +tert-amyl methyl ether. Smooth representations of the results are presented and used to construct constant-enthalpy contours on Roozeboom diagrams. Comparisons of the experimental results with estimates based on the Flory theory of mixtures are also described.     

Stereoselective reaction between alkyl propiolates and phenols in the presence of sodium azide in tert-butyl alcohol

Abstract  

Stereoselective reaction of various substituted phenols with alkyl propiolates in the presence of a catalytic amount of sodium azide in tert-butyl alcohol at reflux temperature leads to alkyl (Z)-3-phenoxy-2-propenoates in good yields.     

New azo-peroxidic initiators in the radical polymerization of styrene and methyl methacrylate

Two new azo-perester compounds, di-tert-butyl-6,6′-azobis-(6-cyanoperoxyheptanoate) (6,6-di-tBu) and di-tert-amyl-6,6′-azobis-(6-cyanoperoxyheptanoate) (6,6-di-tAm), synthesized on the basis of 6,6′-azobis-(6-cyanoheptanoic acid) (ACHpA), were investigated for their use in the radical polymerization of styrene (S) and methyl methacrylate (MMA). Their characteristics are given, including chemical (IR spectra), thermal (DSC) and kinetic, i.e., thermal decomposition studied by volumetric and gas chromatographic methods. The rate constants and activation energies of the decomposition of both the azo and perester bonds were determined. The new azo-peresters were utilized to initiate the radical solution polymerizations of S and MMA at 60 °C. The kinetic parameters of the processes, i.e., polymerization rate and overall rate constant, were determined. Subsequently, the polymerization products were characterized by IR and DSC. It was found that the perester groups were present in the obtained polymers, and hence, the polymers are “active” for further polymerization.     

Synthesis of 2,2′-diamino-7-tert-butyl-9,9′-spirobifluorene starting from 4,4′-di-tert-butylbiphenyl

Abstract  

A novel spirobifluorene diamine monomer, 2,2′-diamino-7-tert-butyl-9,9′-spirobifluorene, was obtained starting from the readily available reagent 4,4′-di-tert-butylbiphenyl. The key step of the synthesis is the introduction of a nitro group into the 2-position of the spirobifluorene through the loss of tert-butyl at the 2-position.     

Synthesis and Phosphorylation of 4-Functionalized 2-tert-Butyl-3-chloromethylfurans

3-Ethoxycarbonyl-, 3-acetyl-2-methyl-5-tert-butylfurans undergo chloromethylation underthe unusually rigorous conditions (55-60°C, 3-3.5 h). The corresponding diethylamide and nitrile were prepared by standard modification of the carboxy group. In phosphorylation of the resulting chloromethylfurans under the conditions of the Michaelis-Becker reaction, in the case of the ester and diethylamide, the phosphonate yields were close to those obtained with compounds containing no tert-butoxy group, and in the case of acetylfuran the yield was even somewhat higher. On the contrary, the chloromethylated nitrile reacts considerably more slowly than all the other compounds under consideration and than the similar compound containing no tert-butyl substituent. Thus, the effect of the tert-butyl group in the -position of the furan ring is clearly pronounced in the electrophilic substitutions in the neighboring position of the heteroring. When the reaction center is located in the side chain (substitution of chlorine), the effect of the bulky substituent is manifested only in special cases and can be attributed to the presence of a conformation in which the chloromethyl group is shielded.     

Synthesis and polymerization of p-(p′-vinylbenzoyl)-peroxybenzoic acid tert-butylester: A monomer containing a photodissociable radical source

In a previous report we have shown that efficiently photodecomposable, but thermally stable, peresters can be made from a compound that contains both a triplet photosensitizer functionality and a perester group. This fundamental approach has been extended to make a novel vinyl monomer containing a triplet sensitizer and a perester group. Thus, the monomer p-vinylbenzoyl-p-tert-butyl perbenzoate (VBPE) has been synthesized and polymerized by normal procedures without loss of perester activity. The resulting polymer perester can be used as an efficient photolabile radical source by irradiating at the λ_max of the benzophenone carbonyl moiety. The homopolymer (PVBPE) and copolymers with other monomers, such as styrene, could be photocrosslinked with high efficiency. Copolymers of VBPE and styrene containing low percentages of VBPE have been used to initiate graft chains of poly(methyl methacrylate) by irradiating a solution of the copolymer in methyl methacrylate at 366 nm.     

Synthesis and Phosphorylation of 2- and 3-Halomethyl Derivatives of Functionalized 2-tert-Butylfurans

2-Halomethyl derivatives of 3-functionalized 5-tert-butylfurans are phosphorylated underconditions of the Michaelis-Becker, Arbuzov reactions similarly to other halomethylfurans. No effectof the tert-butyl substituent on the yield of the reaction products was found in this case. Contrary to that, the2-methoxymethyl derivative of 3-chloromethyl-5-tert-butylfuran proved to be more thermostable than its analog containing no tert-butyl substituent. As a result, the yield of phosphonate in the Michaelis-Becker reaction under similar conditions increases 2.5 times. The observed stabilization of the furan ring is explained by shielding of its oxygen atom by the tert-butyl group.     

Regioselective vinylation of kojic acid using acetylenic esters in the presence of triphenylphosphine or tert-butyl isocyanide

Abstract  

The 1:1 reactive intermediates generated by addition of tert-butyl isocyanide or triphenylphosphine to acetylenic esters were trapped by kojic acid to yield O-vinylated and C-vinylated kojic acid, respectively.     

Synthesis and cytotoxic activity of derivatives of the <Emphasis Type="Italic">tert</Emphasis>-butyl ester of 7<Emphasis Type="Italic">Z</Emphasis>-acetylmethylene-3-methyl-3-cephem-4-carboxylic acid

The condensation of the acetylmethylene group in the tert-butyl esters of 7Z-acetylmethylene-3-methyl-3-cephem-4-carboxylic acid and 7Z-acetylmethylene-3-methyl-1,1-dioxo-3-cephem-4-carboxylic acid and in 7Z-acetylmethylene-3-methylene-1,1-dioxo-3-cephem with arylmethoxyamines and O-alkylation of the tert-butyl ester of 7Z-(2-hydroxyimino)propylidene-3-methyl-1,1-dioxo-3-cephem-4-carboxylic acid using substituted benzyl bromides as well as pyridylmethyl chlorides gave arylmethoxyimino and pyridylmethoxyimino derivatives of these compounds in the syn and anti isomeric forms. The Vilsmaier reagent was used to introduce the N,N-dimethylaminomethylene group at C-2 of the cephem system in the tert-butyl esters of 7Z-[2-(arylmethoxyimino)propylidene]-3-methyl-1,1-dioxo-3-cephem-4-carboxylic acid. Subsequent transformation of the N,N-dimethylaminomethylene cephems using hydroxylamine led to 3Z-[2-(anti-arylmethoxyimino)propylidene]-tert-butoxycarbonylmethyl-4-(5-methyl-4-isoxazolylsulfonyl)- azetidin-2-ones. Condensation of the acetyl group in the tert-butyl ester of 7Z-acetylmethylene- 3-methyl-1,1-dioxo-3-cephem-4-carboxylic acid with 4-bromophenylhydrazine gave a cephem with a 2-(4-bromophenylhydrazono)propylidene group at C-7. Acylation of the tert-butyl ester of 7Z-(2-hydroxyimino)propylidene-3-methyl-1,1-dioxo-3-cephem-4-carboxylic acid by 2-bromobenzoyl chloride gave a cephem with a 2-(2-bromo-benzoyloxyimino)propylidene group at C-7. Biological screening of these products towards to malignant and normal cells in vitro showed that their antitumor activity and cytotoxic selectivity towards to malignant and normal cells depend on the structure and configuration of the arylmethoxyimino and pyridylmethoxyimino groups in the 7-alkylidene substituent as well as on the presence or absence of N,N-dimethylaminomethylene and carboxyl groups, respectively, at C-2 and C-4 of the cephem system.     

Opening and Addition Modes in Propagation During Radical Polymerization of Fumaric and Maleic Derivatives

Abstract

Polymers of bis(trimethylsilyl) fumarate, di-tert-amyl fumarate, and methyl tert-amyl fumarate were prepared by radical polymerization at 60 or 120°C. The polymers were converted into poly(dimethyl fumarate) via thermolysis or hydrolysis and subsequent methylation to determine the tacticity using ¹³C-NMR spectroscopy. The probabilities of meso addition (P _m) were revealed to be 0.66 (60°C) for the bis(trimethylsilyl) ester, 0.60 (60°C) and 0.52 (120°C) for the di-tert-amyl ester, and 0.54 (60 and 120°C) for the methyl tert-amyl ester. From the temperature dependence of the P _m values, the differences in activation enthalpies and entropies for the meso and racemo additions were evaluated. The microstructure of poly(dimethyl fumarate) derived from poly(maleic anhydride) was also examined. The opening and addition modes in propagation of the fumaric and maleic derivatives were discussed based on the results obtained in the present and previous work.     

Thermochemical Studies for Determination of the Standard Molar Enthalpies of Formation of Alkyl-Substituted Furans and Some Ethers

The standard molar enthalpies of vaporization _l ^g H _m ^º of 2,5-dimethylfuran, 2-tert-butylfuran, 2,5-di-tert-butylfuran, cyclopentenyl methyl ether, cyclohexenyl methyl ether, and tert-amyl methyl ether were obtained from the temperature variation of the vapor pressure measured in a flow system. The standard (p° = 0.1 MPa) molar enthalpies of formation _f H _m ^º (1) at the temperature T = 298.15 K were measured using combustion calorimetry for 2,5-dimethylfuran, 2-tert-butylfuran, and 2,5-di-tert-butylfuran. From the derived standard molar enthalpies of formation for gaseous compounds, ring correction terms and non-nearest neighbor interactions useful in the application of the Benson group additivity scheme were calculated.     

Determination of lipids and their oxidation products by IR spectrometry

We proposed a procedure for the IR spectrometric determination of lipid hydroperoxides in biological systems. The main bands in the IR absorption spectra of linoleic acid and its hydroperoxide were identified, and analytical bands suitable for the determination of both compounds in their mixtures were selected. It was demonstrated that tert-butyl hydroperoxide can be used as an external standard for determining fatty acid hydroperoxides. Using the external standard method (calibration curve) for tert-butyl hydroperoxides, we calculated the concentration of linoleic acid hydroperoxide in its mixture with linoleic acid; it agreed with the specified values. Using the developed procedure, we estimated the concentration of hydroperoxide groups in natural cardiolipin. The results were compared to those obtained by an independent method (activated chemiluminescence).     

Reaction of Tri- and Tetrasubstituted Alkenes with the Low-Temperature Oxidizing System Aluminum tert-Butylate-tert-Butyl Hydroperoxide

The system consisting of aluminum tert-butylate and tert-butyl hydroperoxide under mild conditions (20°C) oxidizes tri- and tetrasubstituted ethylenes containing at least one -methyl group. The reaction proceeds via formation of tertiary allylic hydroperoxides and their subsequent transformations into unsaturated alcohols and epoxy alcohols, and also into carbonyl compounds. The presence of the latter products suggests degradation of the carbon skeleton of alkenes.     

Surface modification of a silicate substrate by a “grafting from” methodology utilizing a perester initiator

The perester silane t-butyl peroxy-11-trichlorosilylundecanoate was synthesized by hydrosilylation of t-butyl peroxy-10-undecanoate with trichlorosilane. These radical initiators were covalently bound to the surface of silicate substrates by self-assembled monolayer (SAM) techniques. Several hydrophilic and hydrophobic acrylate monomers were successfully grafted onto the silicate substrate by in situ polymerization from the surface bound perester initiators. The polymer brushes were characterized by the ATR-IR, XPS, AFM and water contact angles. The results of the study indicate this “grafting from” technique can be used for the preparation of polymer layers with high graft density. While these surface-bound initiators function similarly to surface-bound azo initiators, the preparation of the surface-active perester is a simple, two-step synthesis.     

Synthesis and Biological Activity of Some Trifluoromethyl Derivatives of 5-tert-Butyl-2-furylmethylideneanilines and Their Silyl Analogs

We have synthesized the corresponding aldimines by condensation of 5-tert-butylfurfural and its trimethyl- and triethylsilyl analogs with 2-, 3-, and 4-trifluoromethylanilines in the presence of 4 molecular sieves. We have studied their neurotropic and antitumor activity. The phenamine motor activity test showed that tert-butyl derivatives exhibit high efficacy and also shorten the ethanol narcosis time. Some silyl derivatives exhibit significant anti-corazole activity. The tert-butyl derivatives have high cytotoxicity toward human lung fibrosarcoma cells (the 3-trifluoromethyl-substituted derivative) and mouse hepatoma cells (the 2-trifluoromethyl-substituted derivative).     

Thermal elimination of isobutene from meta and para tert-di-butyl pyromellitic acid

An investigation of the kinetics of the thermal elimination of isobutene from the meta and para isomers of the tert-butyl diesters of pyromellitic acid has been carried out using Fourier transform-Raman spectroscopy and mass spectroscopy. These studies indicate that the elimination of the tert-butyl group occurs at a temperature 26°C lower for the meta isomer than for the para isomer; the maximum rate of elimination occurs at 184°C for the former and at 210°C for the latter. Analysis of the Raman spectra of the compounds indicates that this effect results from the better packing arrangement in the para monomer compared with the meta monomer. Formation of pyromellitic dianhydride in the tert-butyl diesters of pyromellitic acid occurred only after formation of the pyromellitic acid; thus it occurred at lower temperatures for the meta isomer. When the meta and para tert-butyl diesters of pyromellitic acid are dissolved at 1% concentration in poly (vinyl acetate), the elimination of isobutene occurs at 173°C for both isomers, indicating that it is the differences in crystal packing which give rise to the 26°C difference in the solid-state samples. For the meta, para, and 50/50 mixed isomers of the tert-butyl esters of oxydianiline/pyromellitic dianhydride polyamic acid, the elimination of the tert-butyl group occurs at the same temperature (177°C). This result indicates that the packing arrangement of the tert-butyl group is disrupted in the polymer chain, so that intermolecular bonding does not hinder thermal deprotection of the tert-butyl group from the polymer. © 1992 John Wiley & Sons, Inc.     

Thermal decomposition of the tert-butyl perester of thymidine-5′-carboxylic acid. Formation and fate of the pseudo-C4′ radical

Thermal decomposition of the tert-butyl perester of thymidine-5′-carboxylic acid 1 carried out at 85 °C in different solvents affords the tert-butylacetal 4a, deriving from in cage decomposition, and pseudo C4′ radicals 2. Radicals 2 can be reduced to 5 by hydrogen atom abstraction from thiol (thiophenol or glutathione) or THF, or can be oxidized to cations 8 by dioxygen or perester 1 itself. Cations 8 are stereoselectively trapped by the nucleophilic solvent (tert-butanol, methanol, water) to give acetals 4a-c.     

Photostabilizing activity of N-acylated hindered amine

The influence of the acyl groups of N-acylated hindered amine on the photostabilization of polymers was discussed. The effects of the N-acyl derivatives of 4-benzoyloxy-2,2,6,6-tetramethylpiperidine ( 6 ) in the photostabilization of polypropylene were compared. Although the stabilizing effects of all the N-acyl derivatives were lower than that of the N-oxyl derivative ( 7 ), N-acryloyl ( 4 ) and N-benzoyl ( 5 ) derivatives showed higher effects than that of parent N? H 6 . To discuss the stabilizing mechanism of N-acylated hindered amine, the reaction of N-acylated hindered amine with model hydroperoxide (tert-butyl hydroperoxide) was carried out at an elevated temperature (132°C). N-Acylated hindered amine decomposed tert-butyl hydroperoxide more rapidly than corresponding secondary hindered amine, and changed into the parent secondary amine.