Phenol-4-carbonic acid esters

Protection of phenol groups as carbonic acid esters s. 18, 259... 

Amongst heat stabilisers are copper salts, phosphoric acid esters,phenyl-3-naphthylamine, mercaptobenzothiazole and mercaptobenzimidazole. Of these, copper salts in conjunction with halides have been found particularly effective, and some automotive specifications require the use of copper for heat stabilisation. Light stabilisers include carbon black and various phenolic materials. 

Still another possibility in the base-catalyzed reactions of carbonyl compounds is alkylation or similar reaction at the oxygen atom. This is the predominant reaction of phenoxide ion, of course, but for enolates with less resonance stabilization it is exceptional and requires special conditions. Even phenolates react at carbon when the reagent is carbon dioxide, but this may be due merely to the instability of the alternative carbonic half ester. The association of enolate ions with a proton is evidently not very different from the association with metallic cations. Although the equilibrium mixture is about 92 % ketone, the sodium derivative of acetoacetic ester reacts with acetic acid in cold petroleum ether to give the enol. The Perkin ring closure reaction, which depends on C-alkylation, gives the alternative O-alkylation only when it is applied to the synthesis of a four membered ring ... 

The chemical diversity of carboxylic acid esters (R-CO-O-R ) originates in both moieties, i.e., the acyl group (R-CO-) and the alkoxy or aryloxy group (-OR7). Thus, the acyl group can be made up of aliphatic or aromatic carboxylic acids, carbamic acids, or carbonic acids, and the -OR7 moiety may be derived from an alcohol, an enol, or a phenol. When a thiol is involved, a thioester R-CO-S-R7 is formed. The model substrates to be discussed in Sect. 7.3 will, thus, be classified according to the chemical nature of the -OR7 (or -SR7) moiety, i.e., the alcohol, phenol, or thiol that is the first product to be released during the hydrolase-catalyzed reaction (see Chapt. 3). Diesters represent substrates of special interest and will be presented separately. 

Polycarbonates are polyesters of carbonic acid. The most important commercial polycarbonate is that based on 2,2 -bis(4-hydroxyphenyl)propane(bisphenol A) [Freitag et al., 1988 Sehanobish et al., 1996]. It has been synthesized by the reaction of the dihydric phenol with phosgene or by ester interchange with diphenyl carbonate ... 

Alcohols and phenols can be attached to support-bound alcohol linkers as carbonates [467,665,666], although few examples of this have been reported. For the preparation of carbonates, the support-bound alcohol needs to be converted into a reactive carbonic acid derivative by reaction with phosgene or a synthetic equivalent thereof, e.g. disuccinimidyl carbonate [665], carbonyl diimidazole [157], or 4-nitrophenyl chloro-formate [467] (see Section 14.7). The best results are usually obtained with support-bound chloroformates. The resulting intermediate is then treated with an alcohol and a base (DIPEA, DMAP, or DBU), which furnishes the unsymmetrical carbonate. Carbonates are generally more resistant towards nucleophilic cleavage than esters, but are less stable than carbamates. Aryl carbonates are easily cleaved by nucleophiles and are therefore of limited utility as linkers for phenols. 

The flask contained 700.0 mg hydroxocobalamin in 20 ml of water, one funnel 200.0 mg sodium borohydride in 10 ml of water, and another the crude isopropylidine adenosine tosyl ester made from 500 mg isopropylidine adenosine dissolved in 10 ml of 50% aqueous methanol. On adding the borohydride to the vitamin, the color changed instantly from red to brown, then slowly to a greenish black. After 15 min the isopropylidine adenosine tosyl ester was added, and the colour slowly changed to a red-brown. After 45 min at room temperature air was admitted and the mixture was shaken to reoxidise any remaining reduced vitamin B12. The alkaline solution was neutralized with dilute hydrochloric acid and extracted with phenol carbon tetrachloride 3 1 in small portions till the aqueous layer was nearly colorless. The combined extracts were washed with water, mixed with about ten parts of carbon tetrachloride-acetone 10 1 and shaken with small portions of water till all red color was removed. 

Four main types of antioxidants are commonly used in polypropylene stabilizer systems although many other types of chemical compounds have been suggested. These types include hindered phenolics, thiodi-propionate esters, aryl phosphites, and ultraviolet absorbers such as the hydroxybenzophenones and benzotriazoles. Other chemicals which have been reported include aromatic amines such as p-phenylenediamine, hydrocarbon borates, aminophenols, Zn and other metal dithiocarbamates, thiophosphates, and thiophosphites, mercaptals, chromium salt complexes, tin-sulfur compounds, triazoles, silicone polymers, carbon black, nickel phenolates, thiurams, oxamides, metal stearates, Cu, Zn, Cd, and Pb salts of benzimidazoles, succinic acid anhydride, and others. The polymeric phenolic phosphites described here are another type. 

Polycarbonates and Polyurethanes The chemistry of carbonic acid derivatives is particularly important because two large classes of polymers are bonded by linkages containing these functional groups the polycarbonates and the polyurethanes. Polycarbonates are polymers bonded by the carbonate ester linkage, and polyurethanes are polymers bonded by the carbamate ester linkage. Lexan polycarbonate is a strong, clear polymer used in bulletproof windows and crash helmets. The diol used to make Lexan is a phenol called bisphenol A, a common intermediate in polyester and polyurethane synthesis. 

Reactions catalyzed by transition-metal complexes allow the synthesis of a variety of esters ruthenium(II) promotes the addition of acids to alkynes,379 380 e.g. 2,6-difluorobenzoic acid (9) undergoes addition to but-l-en-3-yne to furnish the enol ester 10.380 Aryl bromides381 and aryl or vinyl triflates,382-384 but also aryl chlorides when their tricarbonylchromium(O) complexes are used,385 react with palladium382- 385 or cobalt complexes38 to form a C —M bond. Insertion of carbon monoxide into the carbon-metal bond followed by trapping with an alcohol or phenol leads to ester formation, e.g. triflate 11 gives ester 12.382... 

Esters.—While not true alcohols, the phenols nevertheless possess alcoholic character as already referred to in speaking of their similarity to tertiary alcohols. This is shown in their formation of both esters and ethers. Esterification is as a rule less easy than with alcohols. Phenolates absorb carbon dioxide directly yielding a compound that is a mixed ester and salt of carbonic acid. 

In all of these cases the carboxyl group results from the direct introduction of carbon dioxide in front of a hydrogen or sodium atom. Now the sodium compound of phenol, viz., sodium phenolate, CeHg—ONa, undergoes a similar reaction yielding first a phenyl ester of carbonic acid which rearranges into salicylic acid. 

Examples of copolymers with practical use between two different carbonates are poly[2,2-propanebis(4-phenyl)carbonate]-Woc/c-poly[2,2-propanebis[4-(2,6-dimethylphenyl)]carbonate], poly [1,1-cyclohexane bis(4-phenyl)carbonate]-co-[2,2-propane bis(4-phenyl)carbonate], and poly [1,1-dichloroethylene bis(4-phenyl)carbonate]-co-[2,2-propane bis(4-phenyl)carbonate]. Examples of copolymers between a carbonate and an ester are poly[4,4 -(1-methylethylidene)bis[phenol]-co-1,3-benzenedicarboxylic acid-co-carbonic acid], poly[4,4 -(1-methylethylidene)bis[phenol]-co-1,4-benzenedicarboxylic acid-co-carbonic acid], etc. Other known copolymers include poly[2,2-propanebis(4-phenyl)carbonate]-b/oc/(-poly(ethylene oxide), poly[2,2-propanebis(4-phenyl)carbonate]-Woc/c-polysulfone, poly[2,2-propanebis(4-phenyl)carbonate]-b/oc/c-poly(dimethylsiloxane), poly[2,2-propanebis(4-phenyl)carbonate]-b/oc/c-poly(methyl methacrylate), etc. These copolymers have in general good thermal resilience and decompose similarly to other polycarbonates [23]. 

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