P-Hydroxybenzoic acids

This may be determined roughly by treating a small test portion with 3-4 ml. of hot water and acidifying with concentrated hydrochloric acid the absence of a precipitate in the warm solution indicates the essential completeness of the reaction. Salicylic acid is sparingly soluble and p-hydroxybenzoic acid is relatively soluble under these conditions. 

Treatment of p hydroxybenzoic acid with aqueous bromine leads to the evolution of carbon dioxide and the formation of 2 4 6 tnbromophenol Explain... 

Small amounts of amyl alcohol have been purified by esterifying with p-hydroxybenzoic acid, recrystallising the ester from CS2, saponifying with ethanolic-KOH, drying with CaS04 and fractionally distilling [Olivier Reel Trav Chim Pays-Bas 55 1027 1936],... 

The homopolymers of p-hydroxybenzoic acid have such a high value for the that they are somewhat intractable. Useful materials may, however, be made by copolymerising with a view to introducing some molecular flexibility or reducing chain packing or introducing some non-linear links. Commercially important liquid crystal polyesters are discussed in Chapter 25. 

In the 1960s the Carborundum company introduced the polymer Ekonol P-3000. This was the polymer of p-hydroxybenzoic acid (I) Figure 25.22), in practice produced by the self-ester exchange of its phenyl ester to prevent decarboxylation. A blend with PTFE, Ekonol T-4000, was also produced. 

Polymers based on these structures became available as Victrex SRP (ICI), Vectra (Hoechst) and Xydar (Amoco). It is reported that the Vectra materials are based on p-hydroxybenzoic acid and hydroxynaphthoic acid monomers, whilst Xydar is based on terephthalic acid, p-hydroxybenzoic acid and pp -dihydrox-ybiphenyl. Whilst properties vary between grades, in general they possess the following outstanding properties ... 

This with potassium hydroxide in methanol forms de-OiV-dimethylarmepavine, m.p. 86-7°, (B. HCl, m.p. 229-30°) of which the methiodide, m.p. 233-4°, on treatment with alkali decomposes into trimetHylamine and a -p-anisyl-/3-(3 4-dimethoxy- 6 - vinylphenyl) -ethylene, m.p. 79°. The latter is oxidised by permanganate in acetone to anisic and m-hemipinic acids. With ethyl sulphate and alkali, armepavine gives 0-ethylarmepavine, an oil, which permanganate oxidises to p-ethoxybenzoic acid. Armepavine is similarly oxidised to p-hydroxybenzoic acid and l-keto-6 7-dimethoxy-2-methyl-1 2 3 4-tetiahydrowoquinoline and is therefore 6 7-dimethoxy-l-p-hydroxybenzyI-2-methyI-l 2 3 4-tetrahydrowoquinoline, i.e., it is laudanosine (p. 187) with MeO. at C replaced by H and MeO at C changed to HO. ... 

Alkali fusion of the metabolite furnished p-hydroxybenzoic acid in good yield as the only isolable product. Vigorous nitric acid oxidation of M gave a high yield of picric acid. Both degradation products must have arisen from the same site, which can be represented by part structure V. While positions 3 and 5 are probably unsubstituted, the vigorous nature of the degradations allows that those at 2 and 6 could bear carbon atoms. 

It must finally be kept in mind that it is extremely easy to adjust the properties of polyesters to desired values by adding small quantities (usually less than 10%) of comonomers in starting monomer feed. Isophthalic, adipic, dodecanedioic, p-hydroxybenzoic acids or esters and diethylene glycol, cyclohexanedimethanol, or bisphenol-A are often used for this purpose. Examples of property adjustment are the modification of solvent diffusivity of PET membranes by the addition of low levels of isophthalate or naphthalene dicarboxylate units in polymer chains139... 

Oxabicydo[2.2.2]octan-3-one 50, which is readily prepared by hydr(>genation of p-hydroxybenzoic acid followed by dehydration40 , can be polymerized by heating with phosphoric acid or sodium hydride to give a polyester23 . jn contrast, 6-oxabi-... 

Bromomethyl-3-methylquinoxaline (273) and m-hydroxybenzoic acid (274) gave either 2-(m-hydroxybenzoyloxymethyl)-3-methylquinoxaline (275) [KOH (1 mol), EtOH, reflux, 2h 69%] or 2-(m-carboxyphenoxymethyl)-3-methylquinoxaline (276) [KOH (2 mol), EtOH, 50°C—>reflux, 1 h 44%] p-hydroxybenzoic acid reacted similarly but o-hydroxybenzoic acid (salicylic acid) gave only the isomer of product (275) even in the presence of KOH (2 mol). It would seem that the substrate (275) preferred to react at the phenolic anion rather than at the carboxylate anion when both were present... 

Sodium or potassium phenoxide can be carboxylated regioselectively in the para position in high yield by treatment with sodium or potassium carbonate and carbon monoxide. Carbon-14 labeling showed that it is the carbonate carbon that appears in the p-hydroxybenzoic acid product. The CO is converted to sodium or potassium formate. Carbon monoxide has also been used to carboxylate aromatic rings with palladium compoimds as catalysts. In addition, a palladium-catalyzed reaction has been used directly to prepare acyl fluorides ArH —> ArCOF. ... 

Esters of aromatic acids are not reduced by this procedure, so an aromatic COOH group can be reduced in the presence of a COOR group. However, it is also possible to reduce aromatic ester groups, by a variation of the trichlorosilane procedure. The o- and p-hydroxybenzoic acids and their esters have been reduced to cresols (HOC6H4CH3) with sodium bis(2-methoxyethoxy)aluminum hydride, NaAlH2(0C2H40Me)2 Red-Al). ... 

The effect of incorporating p-hydroxybenzoic acid (I) into the structures of various unsaturated polyesters synthesised from polyethylene terephthalate (PET) waste depolymerised by glycolysis at three different diethylene glycol (DEG) ratios with Mn acetate as transesterification catalyst, was studied. Copolyesters of PET modified using various I mole ratios showed excellent mechanical and chemical properties because of their liquid crystalline behaviour. The oligoesters obtained from the twelve modified unsaturated polyesters (MUP) were reacted with I and maleic anhydride, with variation of the I ratio with a view to determining the effect on mechanical... 

Benzoic acid and esters of p-hydroxybenzoic acid Bronopol Chlorhexidine Formaldehyde Glutaraldehyde Halogens Hexachlorophane Mercurials... 

Among the hydroxycinnamic acids, anthocyanins acylated with sinapic acid are not widespread in foods they have been isolated only in black carrots " and red cabbages." Anthocyanins that are acylated with p-hydroxybenzoic acid were only found in black carrots " and sweet potatoes. This acyl group was located within the 6 position of a glucoside moiety. 

The total phenolic content in XRPP was 1.10%. The major components were found to be p-hydroxybenzoic acid (0.44%), vanillin (0.19%), syringic acid (0.13%), and syringaldehyde (0.13%). The contents of p-hydroybenzaldehyde, vanillic acid and ferulic acid were 0.032, 0.015 and 0.020%, respectively. Gallic acid, protocatechuic acid and cinnamic acid were detected in trace amounts. 

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