Acetate esters, decomposition

The addition of 2-diazopropane or 3-diazopentane to (112) results in exo-endo mixtures of both the triazoline (113) and the bicyclo[2.1,0]pentane (114). However, with the 1,2,3,4-tetramethyl analogue of (112) no addition occurs, Surprisingly, the imide (115) incorporates two and three molar equivalents of methylene from diazomethane to give products of spirocyclopropanation at C-4. Monocyclopropana-tion of (116) at the least substituted double bond proceeds efficiently when diazo-acetic ester decomposition is catalysed by copperfn) and similar monoaddition to... 

Intermediate 37 can be transformed into ( )-thienamycin [( )-1)] through a sequence of reactions nearly identical to that presented in Scheme 3 (see 22— 1). Thus, exposure of /(-keto ester 37 to tosyl azide and triethylamine results in the facile formation of pure, crystalline diazo keto ester 4 in 65 % yield from 36 (see Scheme 5). Rhodium(n) acetate catalyzed decomposition of 4, followed by intramolecular insertion of the resultant carbene 3 into the proximal N-H bond, affords [3.2.0] bicyclic keto ester 2. Without purification, 2 is converted into enol phosphate 42 and thence into vinyl sulfide 23 (76% yield from 4).18 Finally, catalytic hydrogenation of 23 proceeds smoothly (90%) to afford ( )-thienamycin... 

A third category of syn eliminations involves pyrolytic decomposition of esters with elimination of a carboxylic acid. The pyrolysis of acetate esters normally requires temperatures above 400° C and is usually a vapor phase reaction. In the laboratory this is done by using a glass tube in the heating zone of a small furnace. The vapors of the reactant are swept through the hot chamber by an inert gas and into a cold trap. Similar reactions occur with esters derived from long-chain acids. If the boiling point of the ester is above the decomposition temperature, the reaction can be carried out in the liquid phase, with distillation of the pyrolysis product. 

A third category of syn eliminations involves pyrolytic decomposition of esters with elimination of a carboxylic acid. The pyrolysis of acetate esters normally requires temperatures above 400° C. The pyrolysis is usually a vapor-phase reaction. In the... 

Reactions conducted in molten quaternary phosphonium salts require no other solvent (199). This material serves as both promoter and reaction medium. Care must be exercised in choosing the salt in such a reaction, since any decomposition could lead to products such as trialkylphosphines and alkyl halides which are expected to be deleterious to catalyst performance. Tetrabutylphosphonium bromide is reported to provide a stable catalyst medium which can be recycled (199, 200), but other related salts show evidence of thermal decomposition during catalytic reactions. Experiments in tetrabutylphosphonium acetate, for example, are found to produce large amounts of methyl and ethylene glycol acetate esters (199). 

The tinctura iodi of the British Pharmacopoeia is a soln. of half an ounce of iodine, and a quarter of an ounce of potassium iodide in a pint of rectified spirit. P. Wantig found the mol. ht. of soln. —1 941 Cals., and S. U. Pickering —1 714 per 880 mol. of ethyl alcohol. C. Lowig found that alcoholic tincture of bromine is slowly decomposed in darkness, rapidly in light. Alcoholic soln. of iodine, according to H. E. Barnard, are stable in light and in darkness, but according to J. M. Eder they decompose 1000 times more slowly than chlorine water under similar conditions T. Budde has shown that hydriodic acid, acetic ester, and aldehyde are formed, and the electrical conductivity of the soln. increases. J. H. Mathews and E. H. Archibald and W. A. Patrick found a freshly prepared AT-soln. to have an electrical conductivity of 2 4 XlO-6 reciprocal ohms and a sat. soln., 1 61 X10 4 reciprocal ohms at 25°. The decomposition is accelerated by the presence of platinum. The heat of soln. decreases with concentration from —7 92 to —7 42 cals, respectively for dilute and sat. soln. in methyl alcohol, and likewise from —4 88 to —5 22 cals, for similar soln. in ethyl alcohol. The solubility of iodine in aq. soln. of propyl alcohol is not very different from that in ethyl alcohol. 

Hydrolysis of 63 in concentrated hydrochloric acid at 100 °C for 6 h afforded 95% of uracil diol 65 with H and 13C NMR spectral data virtually identical to those of cylindrospermopsin except for the protons and carbons close to C12. A similar hydrolysis of 64 provided 95% of 66. This hydrolysis is perhaps the most remarkable step in the synthesis. Very harsh conditions are needed to hydrolyze the dimethoxypyrimidine to the uracil. However, the reaction is remarkably clean, accompanied only by the desired hydrolysis of the acetate ester, but no decomposition or epimerization at any of the stereocenters. Presumably, the protonated guanidine and uracil make it hard to protonate either alcohol and solvolyze to form a trication. 

Intermolecular cyclopropanation reactions with ethyl diazoacetate have been employed for the construction of the cyclopropane-containing amino acid 7 (equation 25) Thus, rhodium(II) acetate catalysed decomposition of ethyl diazoacetate in the presence of d-cbz-vinylglycine methyl ester 5 afforded cyclopropyl ester 6 in 85% yield. Removal of the protecting group completed the synthesis of 7. Another example illustrating intermolecular cyclopropanation can be found in Piers and Moss synthesis of ( )-quadrone 8" (equation 26). Intermolecular cyclopropanation of enamide or vinyl ether functions using ethyl diazoacetate has also been used in the synthesis of eburnamonine 9", pentalenolactone E ester 10" and ( )-dicranenone A11" (equations 27-29). 

SAFETY PROFILE Poison by subcutaneous, intravenous, and parenteral routes. Moderately toxic by ingestion. When heated to decomposition it emits very toxic fumes of NOx and CF. A cholinergic agent. See also CHOLINE ACETATE (ESTER). 

The consistancy of the observed /4-factors, the magnitude of the activation entropies, the a correlations in the substituent effects at the a- and /8-carbon positions, the collective influence of all three substitutable centers on the reaction rates, the importance of charge stabilization in the transition state, and the primary deuterium isotope effects on the alkyl acetic acid ester decomposition, all favor the concerted polar 6-center transition state shown below (IV). However, an alternative possibility involving intimate ion-pair formation has been proposed by Scheer et al.. ... 

D(C1-C02R) = 56 kcal.mole" would satisfy the observed kinetics. This value (which seems too low by about 5-lOkcal.mole" ) is certainly a lower limit because surface initiation reactions are undoubtedly also important. The Arrhenius /4-factors observed for the normal elimination reactions to olefin, HCl, and CO2 fluctuate around the transition state estimates and do so probably as a result of experimental errors and reaction complexities. Note that the chloroformic acid, which is the primary elimination product, is very unstable at reaction temperatures and rapidly decomposes, probably by a 4-center transition state, to give HCl -I- CO2 (ref. 159). The experimental reaction rates of the chloroformate ester eliminations are two powers of ten faster than those for the corresponding formate and acetate esters. This is reasonable since electron withdrawing substituents at the (C-1) position accelerate the decompositions. It seems likely, then, that the normal uni-molecular eliminations and the free radical chain decompositions are competitive processes in these chloroformate ester reactions. 

Decompositions ot benzyl acetate" , benzyl benzoate and a series of allyl acetate esters have been studied by the toluene carrier flow technique. First-order kinetics for reactant disappearance or for CO2 formation were assumed to apply to the initial bond rupture processes... 

Diazo-acetic Esters. —Mercuric oxide dissolves in the cooled ethyl ester of diazo-acetic acid, and the product is extracted with ether. From the ethereal solution yellow, rhombic crystals of mercury bis-diazo-aceiic ethyl ester are deposited, the parameters of which are a b c=0-4546 1 0-72527. The crystals melt with decomposition at 104° C., and are affected by direct sunlight, mercury separating out. The substance explodes on concussion and is volatile in steam, with some decomposition. 

The most common polymer of a vinyl ester is poly(vinyl acetate), CAS 9003-20-7, with the formula [-CH2CH(OC(0)CH3)-]n. Other vinyl esters also are known, such as poly(vinyl butyrate), poly(vinyl benzoate) CAS 24991-32-0, and poly(vinyltrifluoroacetate), CAS 25748-85-0. Poly(vinyl acetate) is typically obtained from the monomer with radical initiators, either by emulsion or suspension polymerization. The polymer Is used in water-based emulsion paints, adhesives [22], gum base for chewing gum, etc. Also, poly(vinyl acetate) is used as a precursor for the preparation of other polymers such as poly(vinyl alcohol) or poly(vinyl acetals). Thermal decomposition of poly(vinyl acetate) starts at a relatively low temperature, around 200° C, some of the reports regarding its thermal decomposition being given in Table 6.5.8 [13]. The same table includes references for poly(vinyl butyrate) and poly(vinyl cinnamate), CAS 9050-06-0. 

When a carbene center and a nitrogen are linked by a four-carbon chain, insertion into the N — H bond gives rise to piperidine derivatives. The rhodium(II) acetate-catalyzed decomposition of either diazo ketones 158 (92TL6651) or diazo ester 159 (85JOC5223) leads to insertion into the amide N — H bond to give products in moderate yields. Various solvents, temperatures, and catalyst concentrations were found to be important in determining the yield and the product distribution in the cyclization of 159. 

Rhodium(II) acetate-catalyzed decomposition of diazo ester 677 gives oxacepham 678 via the formation of oxonium ylide 679 and its subsequent fragmentation (91CC1235). 

The reverse trend was found for intramolecular cyclopropanation of a-(alkenyloxysilyl)diazo-acetic esters. For the synthesis of methyl 2,2-diisopropyl-3-oxa-2-silabicyclo[4.1.0]heptane-l-carboxylate (7) from methyl diazo[(but-3-enyloxy)diisopropylsilyl]acetate, the thermal procedure gave the best result. In contrast, the lower homologs, 3-oxo-2-silabicyclo[3.1.0]hexanes, were only obtained by photochemical or catalytic decomposition of the corresponding diazo esters (see also Section 1.2.1.10.). 

Under the conditions of homogeneous catalysis, decomposition temperatures are normally significantly lower than with the heterogeneous catalysts mentioned above, and cyclopropane yields in general are higher. However, catalysts of type 2 must first be converted into the active form [presumably a copper(I) monochelate] by brief heating or by in situ reduction (see Table 10). Another soluble catalyst, copper(I) triflate, even decomposes diazoacetic esters and diazomalonic esters at temperatures below 0 °C and sterically more encumbered diazocarbonyl compounds (e.g. a-diazo-a-trialkylsilyl acetic esters " ) still at room temperature, and has shown its effectiveness in a number of cyclopropanation reactions. Since copper(I) triflate is... 

Because oxidative decarboxylation of carboxylic acids by lead tetraacetate depends on the reaction conditions, the co-reagents, and the structures of the acids, a variety of products such as acetate esters, alkanes, alkenes, and alkyl hahdes can be obtained. Mixed lead(IV) carboxylates are involved as intermediates as a result of their thermal or photolytic decomposition decarboxylation occurs and alkyl radicals are formed. Oxidation of alkyl radicals by lead(IV) species gives carbocations a variety of products is then obtained from the intermediate alkyl radicals and the carbocations. Decarboxylation of primary and secondary acids usually affords acetate esters as the main products (Scheme 13.41) [63]. 

Metal-assisted decompositions of a-diazocarbonyl compounds in 1,2-dialkoxy-l-alkenes give dialkoxycyclopropylcarbonyl systems. Thus, reaction of 2,3-dihydro-1,4-dioxin with ethyl diazoacetate at 80°C over copper bronze yielded the cyclopropane (111) acid catalyzed solvolysis of this with water, and with ethanol, gave hemiacetal and acetal esters (112) and (113), respectively <85JOC4681>. 

METHYL ACETIC ESTER (79-20-9) Forms explosive mixture with air (flash point 14°F/—10°C). Violent reaction with oxidizers. Contact with acids or bases causes decomposition with formation of methanol. Incompatible with nitrates. Attacks some plastics. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

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