Acetates forms

Prepared generally by ester interchange from polyvinylacelate (ethanoate) using methanol and base also formed by hydrolysis of the acetate by NaOH and water. The properties of the poly(vinyl alcohol) depend upon the structure of the original polyvinyl acetate. Forms copolymers. Used as a size in the textile industry, in aqueous adhesives, in the production of polyvinyl acetates (e.g. butynal) for safety glasses. U.S. production 1980... 

Hydrolyse the acetyl-sulphap3Tidine by boiling it with 10 parts of 2N sodium hydroxide for 1 hour, and allow to cool. Precipitate the base by the addition of 50 per cent, acetic acid until the mixture is just acid to litmus (pH about 6 5) avoid a large excess of acid. Filter off the crude sulphapyridine, wash well with water, and dry at 90° to constant weight (about 12 hours any acetate formed will bo decomposed). The yield is 35 g. RecrystaUise from 90 per cent, acetone (5) the recovery of the pure compoimd, m.p. 190-191°, is about 80 per cent. 

Oxidation of ethylene in alcohol with PdCl2 in the presence of a base gives an acetal and vinyl ether[106,107], The reaction of alkenes with alcohols mediated by PdCl2 affords acetals 64 as major products and vinyl ethers 65 as minor products. No deuterium incorporation was observed in the acetal formed from ethylene and MeOD, indicating that hydride shift takes place and the acetal is not formed by the addition of methanol to methyl vinyl etherjlOS], The reaction can be carried out catalytically using CuClj under oxygen[28]. 

Ketal IS an acceptable sub category term for acetals formed from ketones It was dropped from lUPAC nomen clature but continues to be so widely used that it has been reinstated... 

More useful than the preceding methods is cleavage of alkoxides by acetyl chloride or bromide. One, two, three, or four alkoxyls can be replaced by chloride or bromide. Benzoyl chloride gives poor yields, however. The tri- and tetrachlorides, which are stronger Lewis acids than mono- and dichlorides, coordinate with the alkyl acetate formed and yield distillable complexes (46,55,56). 

Vinyl acetate is a colorless, flammable Hquid having an initially pleasant odor which quickly becomes sharp and irritating. Table 1 Hsts the physical properties of the monomer. Information on properties, safety, and handling of vinyl acetate has been pubUshed (5—9). The vapor pressure, heat of vaporization, vapor heat capacity, Hquid heat capacity, Hquid density, vapor viscosity, Hquid viscosity, surface tension, vapor thermal conductivity, and Hquid thermal conductivity profile over temperature ranges have also been pubHshed (10). Table 2 (11) Hsts the solubiHty information for vinyl acetate. Unlike monomers such as styrene, vinyl acetate has a significant level of solubiHty in water which contributes to unique polymerization behavior. Vinyl acetate forms azeotropic mixtures (Table 3) (12). 

In a typical system the reaction vessel is at 75-80°C and the vinyl acetate formed is swept out into a condenser at 72-74°C by means of circulating excess acetylene. This prevents distillation of higher boiling components but allows the vinyl acetate and acetylene through. The former is separated out by cooling and the acetylene recycled. 

A commonly used alternative to the direct bromination of ketones is the halogenation of enol acetates. This can be carried out under basic conditions if necessary. Sodium acetate, pyridine or an epoxide is usually added to buffer the reaction mixture. The direction of enolization is again dependent upon considerations of thermodynamic and kinetic control therefore, the proportion of enol acetates formed can vary markedly with the reaction conditions. Furthermore, halogenation via enol acetates does not necessarily give the same products as direct halogenation of ketones 3. 23... 

Diphenylimidazole with palladium acetate forms the cyclometallated complex 80 (X = OAc) (97AOC491). The acetate group is replaced by chloride or bromide when 80 (X = OAc) reacts with sodium chloride or lithium bromide, respectively, to give 80 (X = C1, Br). Bromide with diethyl sulfide forms the mononuclear complex 81. Similar reactions are known for 1 -acetyl-2-phenylimidazole (96JOM(522)97). 1,5-Bis(A -methylimidazol-2-yl)pen-tane with palladium(II) acetate gives the cyclometallated complex 82 (OOJOM (607)194). 

The two polyalkylpyrroles which have been reported to form a dimer picrate in refluxing ethyl acetate form an interesting problem, and arc briefly discussed on p. 297,... 

Thienylacetarnidocephalosporanic acid (7.0 g) was suspended in water (60 ml) and stirred with pyridine (7 ml) until the acid dissolved. The resulting solution (pH 5.9) was kept at 35°C for 3 days, then filtered and extracted with methylene chloride (4 x 60 ml). The methylene chloride extract was back-axtracted with a little water and the total aqueous solutions were then percolated through a column of Dowex 1x8 resin, (100 to 200 mesh, 150 g) in the acetate form at pH 4.3. The column was washed with water until the optical rotation of the eluate fell to zero and the eluate (500 ml) was freeze-dried. The residual white solid was dissolved in the minimum volume of methanol and after a few minutes the pyridine derivative crystallized this is the cephaloridine product. 

The importance of the proximity effect in cyclodextrin catalysis has been discussed on the basis of the structural data. Harata et al. 31,35> have determined the crystal structures of a-cyclodextrin complexes with m- and p-nitrophenols by the X-ray method. Upon the assumption that m- and p-nitrophenyl acetates form inclusion complexes in the same manner as the corresponding nitrophenols, they estimated the distances between the carbonyl carbon atoms of the acetates and the adjacent second-... 

Glycoside (Section 25.6) A cyclic acetal formed by reaction of a sugar with another alcohol. 

Alkyl A-(3-oxobuten-l-yl)-2-aminobenzyl ketones 9 (as their cyclic acetals), formed by condensation of alkyl 2-aminobenzyl ketones with 3-methoxybut-3-ene-2-one, undergo acid-catalyzed cyclization to give rare examples of A -unsubstituted 1H-1 -benzazepines 10 in high yields.81... 

On the other hand, it has recently been reported (7) that phenyl acetate forms the derived ketene trimethylsilyl acetal by exclusive O-silylation. 

Bromine acetate has also been proposed310 as an intermediate species in the bromination of anisole, phenetole, and methyl p-tolyl ether by 2,4,6-tribromo-N-bromoacetanilide in acetic acid at 25 °C, since this latter compound was stable to both the ethers and to acetic acid, but in the presence of both, bromination of the ethers occurred, presumably via bromine acetate formed as in the equilibrium... 

An (E)-selective CM reaction with an acrylate (Scheme 61) was applied by Smith and O Doherty in the enantioselective synthesis of three natural products with cyclooxygenase inhibitory activity (cryptocarya triacetate (312), cryptocaryolone (313), and cryptocaryolone diacetate (314)) [142]. CM reaction of homoallylic alcohol 309 with ethyl acrylate mediated by catalyst C led (E)-selectively to d-hydroxy enoate 310 in near quantitative yield. Subsequent Evans acetal-forming reaction of 310, which required the trans double bond in 310 to prevent lactonization, led to key intermediate 311 that was converted to 312-314. 

Cyclic acetals formed by the reaction of saccharides or saccharide derivatives with aldehydes or ketones are named in accordance with 2-Carb-24.1, bivalent substituent names (formed by general organic nomenclature principles) being used as prefixes. In indicating more than one cyclic acetal grouping of the same kind, the appropriate pairs of locants are separated typographically when the exact placement of the acetal groups is known. 

Dihexulose dianhydrides are intermolecular cyclic acetals formed by the condensation of two hexulose molecules with the elimination of two water molecules, and the formation of two linkages involving the 2- and one other position of each component. They are named4 by placing the word dianhydride after the names of the two parent monosaccharides. The order of precedence for these... 

The methoxy group of methyl acetate formed during the thermal decomposition of acetyl peroxide appears as an emission, whereas methyl chloride shows enhanced absorption. Consider the reaction sequence in equation (40). 

High modulus blends can be developed by mixing TPU with acetal copolymer (trioxane ethylene oxide copolymers) [242-244]. The highly crystalline acetal forms a second continuous phase. Kumar et al. studied behavior of such blends [245]. TPU retains none of its physical properties after immersion in water at 70°C for three weeks. The hydrolysis resistance of TPU can be improved by blending with polycarbodiimides [246]. Two parts of carbodiimide with TPU offer 87% retention of its strength, 93% of elongation, and 75% of modulus under the same... 

Both starting materials are available, the glycol 2) being a cheap and efficient acetal forming reagent. 

Wang et al. reported that FeCls- and FeBrs-promoted cyclization/halogenation of alkynyl diethyl acetals formed ( )-2-(l-halobenzylidene or alkylidene)-substi-tuted five-membered carbo- and heterocycles. It was found that the 1 1 molar ratio... 

In air at 50 C, vinyl acetate forms a polyperoxide, which detonates on separation. 

When ozone is present, vinyi acetate forms an ozonide that is explosive ... 

Aldehydes can be obtained by reaction of Grignard reagents with triethyl orthoformate. The addition step is preceded by elimination of one of the alkoxy groups to generate an electrophilic oxonium ion. The elimination is promoted by the magnesium ion acting as a Lewis acid.93 The acetals formed by the addition are stable to the reaction conditions, but are hydrolyzed to aldehydes by aqueous acid. 

When this reaction sequence is applied to enol esters or enol ethers, the result is a-oxygenation of the starting carbonyl compound. Enol acetates form epoxides that rearrange to a-acetoxyketones. 

Values of /c2 and Kd for the reactions of the cycloamyloses with a variety of phenyl acetates are presented in Table IV. The rate constants are normalized in the fourth column of this table to show the maximum accelerations imposed by the cycloamyloses. These accelerations vary from 10% for p-f-butylphenyl acetate to 260-fold for m-f-butylphenyl acetate, again showing the clear specificity of the cycloamyloses for meta-substituted esters. Moreover, these data reveal that the rate accelerations and consequent specificity are unrelated to the strength of binding. For example, although p-nitrophenyl acetate forms a more stable complex with cyclohexa-amylose than does m-nitrophenyl acetate, the maximal rate acceleration, h/kan, is much greater for the meta isomer. 

One of the most selective hydroformylation catalysts was obtained when cobalt acetate was irradiated in the presence of an excess of a phosphine, with synthesis gas at 80 atm, in methanol as the solvent. Propylene was hydroformylated with this catalyst to give butyraldehyde with an n/i ratio of more than 99/1 /10/. In the absence of phosphine, the cobalt acetate forms a more active catalyst which is, however, less selective for straight chain products /23/. 

---