Hydroquinone 4-hydroxybenzoate

Kricheldorf H.R., Sun Sh.J., Chen Ch.R, Chang T.Ch., Polymers of carbonic acid. XXIV. Photoreactive, nematic or cholesteric polycarbonates derived from hydroquinone-4-hydroxybenzoate 4,4 -dihydroxychtilcone and isosorbide, J. Polym. Sci. Part A Polym. Chem., 35, 1997, 1611-1619. 

Polycondensations in bulk were also conducted with other silylated diphenols [58, 59], for instance, with hydroquinone 4-hydroxybenzoate ((d) in Formula 7.2). These experiments had the purpose to elucidate, if end-to-end cyclization occurs even in the nematic phase. Liquid-crystalline phases are based on a more or less parallel alignment of the polymer chains, which is the most unfavorable conformation for ring closure. Nonetheless, cyclic oligo-, and polyesters were detected, and interestingly the even-membered rings prevailed largely in contrast to... 

Phenolics may influence competition among plants, a phenomenon called allelopathy. A series of experiments in both the field and the laboratory have indicated a role for a number of phenolic derivatives (hydroquinone, hydroxybenzoates and hydroxycinnamates) as allelopathic agents. These are chemicals excreted by the plant, which may be autotoxic or affect the growth of other plants in the environment [6,7]. 

For the liquid crystal polyesters the basic structural units are derived from such materials as 5-hydroxybenzoic acid, terephthalic acid and hydroquinone. Some basic sequences from such materials are shown in Figure 25.25. 

At alkaline conditions (pH=l 1) no phenol, hydroquinone were detected. This is possibly due to the fact that the rate of phenol oxidation increases under alkaline conditions with optimum pH between 9.5 and 13 [17] and so once it is formed, it is readily oxidised. The absence of phenol and increased concentration of p-hydroxybenzoic acid could be also explained by reduced decarboxylation rates under conditions of high pH, which would result in the oxidation of p-hydroxybenzaldehyde to form p-hydroxybenzoic acid. 

E4 poly[(4-hydroxybenzoic acid)-co-hydroquinone-co-(terephthalic acid)]... 

A paired-ion, reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of sweeteners (dulcin, saccharin-Na, and acesulfame-K), preservatives (sodium dehydroacetate, SA, salicyclic acid, BA, succinic acid, methyl-para-hydroxybenzoic acid, ethyl-para-hydroxybenzoic acid, n-propyl-para-hydroxybenzoic acid, n-butyl-para-hydroxybenzoic acid, and isobutyl-para-hydroxybenzoic acid), and antioxidants (3-tertiary-butyl-4-hydroxyanisole and tertiary-butyl-hydroquinone). A mobile phase of acetonitrile-50 ml aqueous tr-hydroxyisobutyric acid solution (pH 4.5) (2.2 3.4 or 2.4 3.6, v/v) containing 2.5 mM hexadecyltrimethylammonium bromide and a Clg column with a flow rate of 1.0 ml/min and detection at 233 nm were used. This method was found to be very reproducible detection limits ranged from 0.15 to 3.00 p,g. The retention factor (k) of each additive could be affected by the concentrations of hexadecyltrimethylammonium bromide and a-hydroxyisobu-tyric acid and the pH and ratio of mobile phase. The presence of additives in dried roast beef and sugared fruit was determined. The method is suitable for routine analysis of additives in food samples (81). 

Antiseptic plant-derived phenols include phenol (Phe-OH, hydroxybenzene, carbolic acid), />-cresol (4-methylphenol), catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene) and pyrogallol (1,2,3-trihydroxybenzene). Other simple phenols with antimicrobial properties include some related to benzoic acid (benzenecarboxylic acid), namely salicylic acid (2-hydroxybenzoic acid), ginkgoic acid (2-hydroxy-6-(pentadec-8-enyl)benzoic acid), gentisic acid (2,5-dihydroxybenzoic acid), pyrocatechuic acid (3,4-dihydroxybenzoic acid) and gallic acid (3,4,5-trihydroxybenzoic acid). Other plant-derived phenol-related compounds include 4-methylcatechol, 1,3-dihydroxy-5-(heptadec-12-enyl)benzene, hydroquinone (1,4-dihy-droxybenzene), 1,4-dihydroxy-2-geranyl (di-isoprenyl)benzene and 4-methoxybenzaldehyde (/>-anisealdehyde). 

Binding of 4-hydroxybenzoate (S) in the phenolate form facilitates flavin reduction by NADPH. After NADP+ release, the flavin hydroquinone reacts with molecular oxygen to yield the flavin C4a-hydroperoxide oxygenation species. Protonation of the distal oxygen of the peroxflavin facilitates the electrophilic attack on the nucleophilic carbon center of the substrate phenolate. After monooxygenation, the resulting hydroxyflavin is... 

Hydroquinone(HQ) or a naphthalenediol in the above reactions can be replaced with other diols such as biphenols and bisphenols. In the same manner, other dicarboxylic acid such as cyclohexane dicarboxylic acid, isophthalic acid, naphthalene dicarboxylic acids can be used in place of terephthalic acid. Of course, these substitutes should not destroy the linearity of the polymer chains if one is to obtain thermotropic compositions. 6-Hydroxy-2-naphthoic acid is a substitute for 4-hydroxybenzoic acid in Reactions 18 and 19. 

The samples used in the present study are (1) a copolymer consisting of p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) in the mole fraction ratios 73 27 and (2) a polymer which contains HBA, HNA, terephthalic acid (TA) and hydroquinone (HQ) in the ratios 57 41 1 1. It will be shown later that the incorporation of the small amount of TA and HQ into the latter structure makes the material less shear—thinning than the copolymer containing only HBA and HNA, when examined theologically. It is generally believed that a random sequence distribution of monomers occurs in both... 

This catalyst reduces a-naphthol to 1-decalol (94%), which contains 33% cfr,c(s-isomer. Hydroquinone and resorcinol afford 90 and 85% 1,4-cyclohexanediol and 1,3-cycIo-hexanediol, respectively. Hydrogenation of p-hydroxybenzoic acid over Rh-on-alumina to hydroxycyclohexane-4-carboxylic acid is quantitative and 2,2-dimethylben-zofuran affords stereospecifically cw-2,2-dimethyloctahydrobenzofuran in 94% yield . 

The calculation of the MI is still quite straightforward. Suppose a polymer comprises 75% of terephthalic acid/hydroquinone units (TPA/HQ) and 25% m-hydroxybenzoic acid (MHBA). As the corresponding MI scores for the units are 6 (TPA and HQ) and 4 (MHBA) the MI is calculated as follows ... 

Similarly, copolymerization of a certain amount of 4-hydroxybenzoic acid (HBA) with phenyl-1,4-hydroquinone and terephthalic acid also gives rise to a remarkable decrease in the melting point. The general structural formula and the melting points of the copolymers with different HBA content are given respectively by (3.22) and Table 3.6. In this particular case, the incorporation of 20 mol % of HBA into the polymer (3.19) has resulted in a polymer with a melting point as low as 229. 

---