T-butyl Ethers Research Articles

The mechanisms of thermal eliminations. Part 12. Relative rates of pyrolysis of ethyl, isopropyl, t-butyl, and n-butyl vinyl ethers: rate spread as an index of elimination mechanisms

Rate coefficients have been measured between 594.5 and 681.0 K for pyrolysis of ethyl, isopropy, t-butyl, and n-butyl vinyl ethers. The relative rates of elimination at 600 K are : 1.0, 10.0, 178, and 1.52, the Arrhenius data [E/kJ mol–1, log (A/s–1)] being: ethyl, 185.92, 11.826; isopropyl, 182.51, 12.527; t-butyl, 164.05, 12.169; n-butyl, 177.64, 11.284. These results show that the literature data for t-butyl vinyl ether elimination are considerably in error, confirming the prediction based on statistical mechanics. The relative primary, secondary, and tertiary elimination rates are consistent with those obtained from a range of thermal eliminations, whereas the relative rates based on the literature data are not. Analysis of the relative primary, secondary, and tertiary elimination rates from this and other reactions permits prediction of rates for secondary and tertiary compounds as yet unmeasured, and also suggests that some literature data may be in error through the incursion of side reactions. A β-ethyl group increases the rate of elimination 2,3-fold per β-hydrogen at 600 K (cf. 1.62 for acetates) and may likewise be due to steric acceleration, though the possibility of electron acceptance by alkyl groups in the gas-phase cannot be excluded. The product distribution in pyrolysis of 1-methylpropylvinyl ether is shown to be accounted for by the nature of the transition state. Vinyl ethers do not pyrolyse 50° below the corresponding esters as recently claimed. Tertiary vinyl ethers are for example less reactive than tertiary esters.

Alkylation of Butyl Alcohols by Dialkyl Sulfates Using Phase Transfzr Catalysis

Four kinds of butyl alcohols were alkylated by dialkyl sulfates at 4045°C to prepare alkyl butyl ethers using phase transfer catalysts. Experiments were carried aut for pursuing the optimum reaction conditions in the presence of tetrabutylammonium salt, which proved to be most effective among the catalysts tested. It has been found that alkyl n-butyl and isobutyl ethers can be obtained in good yields over 93%, but alkyl s-butyl ethers in about 50% and alkyl t-butyl ethers only in less than 20%.

Synthesis of a 21-residue fragment of human proinsulin by the polyamide solid phase method.

The synthesis of human proinsulin fragment residues 40-60 by a solid phase method based on polydimethylacrylamide is described. Nineteen of the amino-acids were introduced as N alpha-(9-fluorenylmethoxycarbonyl) derivatives; functional side chains were protected as t-butyl ethers and esters. The yield of highly purified 21-residue peptide was 56.5%.

A NEW SYNTHESIS OF ARYL t-BUTYL ETHERS

Abstract Aryl t-butyl ethers were prepared in high yields by O-alkylations of phenols with t-butyl halides in the presence of pyridine or aliphatic amines for a few hours at 20–30 °C.

All ring compounds—XXIX : Thermal decomposition of t-butyl per ( trans-2-substituted cyclopropyl) acetates

Three kinds of t-butyl per ( trans-2-substituted cyclopropyl) acetates (RH, CH 3, C 6H 5) were synthesized from the corresponding acyl chlorides and thermally decomposed in cyclohexane to investigate the chemical stability and behaviour of the cyclopropylcarbinyl radical. Clean first-order kinetics were obtained in all of the thermal decomposition reactions. The experimental fact that the decompositoin rates and activation parameters of these three t-butyl peresters are similar to each other may indicate the absence of the ionic character in the transition state suggesting the almost complete homolytic decomposition of these peresters. Although the typical concerted decomposition might be invalid for these peresters in view of the activation parameters, it would be suggested from the product studies that the decomposition of these peresters was characterized by a considerable loss of their acyl-alky] bonds at the time of the fission of their OO bonds. The products yielded from the thermal decomposition of t-butyl per ( trans-2-phenylcyclopropyl) acetate in various hydrogen donating solvents consisted of three hydrocarbons and two t-butyl ethers. The formation of these t-butyl ethers, possibly cage products, was significant.

Intermediates in the decomposition of aliphatic diazo-compounds. Part VIII. The mechanism of ether formation from diarylmethylenes and alcohols

The thermal decomposition of diphenyldiazomethane and its 4,4′-dichloro-, 4,4′-dimethoxy-, and 4,4′-dimethyl analogues at 85 °C in acetonitrile containing methyl and t-butyl alcohols (ca. 1M) has been studied. Kinetic studies indicate that the major reaction product, the alkyl diarylmethyl ether, is formed by attack of intermediate diarylmethylene on the alcohol. The relative reactivities of methyl and t-butyl alcohols towards the series of diarylmethylenes have been determined: methyl alcohol is the more reactive in all cases, but the difference in reactivity between the two alcohols decreases with increasing electron release by the 4-substituents. By examining the radioactivity of the product ethers formed by reaction of diarylmethylenes with hydroxyl-tritiated alcohols, substantial kinetic isotope effects on ether formation have been detected. The isotope effects are in all cases greater for formation of t-butyl ethers than for methyl ethers. The compatibility of these observations with three possible mechanisms of ether formation has been assessed, and it is concluded that the most likely route is that in which the carbene attacks the oxygen atom of the alcohol to form an ylid which is subsequently transformed by a prototropic rearrangement into the ether.

Structure and reactivity of α,β-unsaturated ethers—IX : The cis-trans isomerization equilibria in the liquid phase

The relative stability of various pairs of cis- and trans-α,β-unsaturated ethers has been determined by geometrical isomerization equilibrium experiments. The isomerization was carried out in bulk in the presence of mercuric acetate at 20 to 50°. The trans isomers of alkenyl and styryl ethyl ethers generally are thermochemically more stable than the corresponding cis ethers by 0·4 to 1·7 kcal/mole. In the case of propenyl alkyl ethers, the methyl, ethyl, and isobutyl ethers are more stable in the trans form, whereas the reverse is true for both the isopropyl and t-butyl ethers. In all these cases, the entropy term favours the stability of the cis ethers. These facts are probably due to the rotational isomerism around the sp 2 CO bond. cis-β-Chlorovinyl and cis-β-ethoxyvinyl ethyl ethers were found to be more stable than the trans isomers.

The thermal decomposition of alkyl vinyl ethers. Part II. The inhibited decompositions of t-butyl, isopropyl, and 2-chloroethyl vinyl ethers

The kinetics of the thermal decompositions of t-butyl, isopropyl and 2-chloroethyl vinyl ethers into predominantly olefins and acetaldehyde in a seasoned vessel have been studied in a static system. These reactions are homogeneous and essentially unimolecular; they obey first-order kinetics in their early stages. The rate constants are: t-butyl vinyl ether (215–324°), k= 1010·86 exp(–36,184/RT); isopropyl vinyl ether (311·0–375·0°), k= 1012·12 exp(–42,557/RT); 2-chloroethyl vinyl ether (353·0–424·0°), k= 1011·49 exp(–44,752/RT) sec.–1.

Thiophene chemistry—XII

3-Acetyl-2-hydroxythiophene and 3-carbethoxy-2-hydroxythiophene have been prepared by acid-catalysed dealkylation of the corresponding t-butyl ethers at 160°. The t-butyl ethers were prepared via organometallic reagents derived from 3-bromo-2-t-butoxythiophene by metal-halogen interconversion with n-butyllithium at −70°. Investigations by NMR and IR spectroscopy show that these 2-hydroxythiophenes exist in the tautomeric hydroxy form in the pure liquid state and in solution. Evidence for the presence of the tautomeric α,β-unsaturated γ-thiolactone form in minute quantities is obtained from the formation of a dimer in the case of 3-carbethoxy-2-hydroxythiophene.

The formation of arynes by reaction of potassium t-butoxide with aryl halides

Potassium t-butoxide reacts with aryl halides in an inert solvent or in the absence of solvent to give arynes in good yield, as indicated by the isolation of mixtures of aryl t-butyl ethers, the isomeric compositions of which have been determined, or, in the case of reactions carried out with added anthracene, of substituted triptycenes.

Thiophene chemistry—X : Preparation, tautomeric structure and hydrogen bonding studies of thioisomaltol (2-acetyl-3-hydroxythiophene) and some related 3-hydroxythiophenes

Different acetyl- and carbethoxysubstituted 3-t-butoxythiophenes have been prepared via organometallic reagents. Dealkylation of these t-butyl ethers in the presence of a catalytic amount of p-toluenesulphonic acid at 150° gives the corresponding 3-hydroxythiophenes in almost quantitative yields. Spectroscopic investigations by NMR and IR show that carbonyl (acetyl or carbalkoxy)-substituted 3-hydroxythiophenes exist exclusively in the hydroxyaromatic form in polar and non-polar media and in the pure (solid or liquid) state. The only exception is 5-carbethoxy-2,3-dihydroxythiophene which is shown to exist in one of is two possible unsaturated γ-thiolactone forms. the NMR and IR-spectra show the presence of hydrogen bonding and when intramolecular hydrogen bonding is sterically possible its strength, as measured by the chemical shft of the enolic proton (NMR) and shifts to lower wave numbers for both the hydroxyl and carbonyl frequencies (IR), is discussed along with observations for compounds with similar structures. Long-range spin coupling between the aromatic C-5 proton and the OH proton is observed in one case.

Synthesis of ethers of ferrocenemethanol

1. The previously undescribed methyl, ethyl, t-butyl, nonyl, decyl, allyl, benzyl, and furyl ethers of ferrocenemethanol were prepared by the action of the alcohols with the methiodide or ethobromide of (dimethylaminomethyl)ferrocene. 2. No rearrangement of the methiodide occurs under the action of sodium hydroxide under the conditions for the preparation of ethers of ferrocenemethanol.