Propyl ester of 4-hydroxybenzoic acid

This part of the chapter describes HPLC techniques for the separation and determination of preservatives, as follows S02, postharvest preservatives (PPs), benzoic acid (BA), sorbic acid (SA), and the ethyl, methyl, propyl esters of 4-hydroxybenzoic acid (EsHBA) and 5-nitrofury-lacrylic acid (5-NFA). The propionic, lactic, acetic acids are discussed in the chapter on organic acids. 

The use of preservative eombinations may be used to extend the range and speetrum of preservation. Thus, in the series of alkyl esters of 4-hydroxybenzoic (/ -hydroxybenzoic) acid (parabens), water solubility deereases in the order methyl, ethyl, propyl and butyl ester. By eombining these produets it is possible to aehieve a situation where both the aqueous and oil phase of an emulsion are proteeted. 

CAS 4247-02-3 EINECS/ELINCS 224-208-8 Synonyms 4-Hydroxybenzoic acid, 2-methyl propyl ester Isobutyl 4-hydroxybenzoate Isobutyl p-hydroxybenzoate Isobutyl parahydroxybenzoate Definition Ester of isobutyl alcohol and p-hydroxybenzoic acid Empirical C11H14O3 Properties M.w. 194.25... 

The parabens are a class of 4-hydroxybenzoic acid esters (primarily methyl, ethyl, propyl, and butyl esters) that are used as biological preservatives in liquid and semisolid dosage forms.Another preservative often used is benzyl alcohol. Parabens and benzyl alcohol are compendial items. These materials are very stable... 

The catalysts were tested in the esterification of 4-hydroxybenzoic acid with propyl alcohol. It was observed that the amount of 4-hydroxybenzoic acid converted into the ester increased continuoirsly with the reaction time. The corrversion depertded strongly on the CF3SO3H content, decreasing from 80 to 7% when Nt, decreased from 0.91 to 0.10 mmol CFsSOsH/g. 

Figure 6.1 UV chromatograms of the test mixture of four / -hydroxybenzoic acid esters (1, methyl 2, ethyl 3, propyl 4, butyl) after the column and after the NMR flow cell at flow rates of (a) 1.0 and (b) 0.1 ml/min conditions column, LiChrospher RP select B, 125 x 4 mm id, 5 Jim, spectrometer, Bruker DRX 600 probe head, 4 mm z-gradient LC probe, active volume 120 a1 eluents, acetonitrile (A) and D2O (B) gradient, t = Omin A/B (40/60), t = 8 min A/B (70/30) at a flow rate of 1.0 ml/min and t = 80 min A/B (70/30) at a flow rate of 0.1 ml/min...

CAS 94-13-3 EINECS/ELINCS 202-307-7 FEMA 2951 INS216 E216 Synonyms 4-Hydroxybenzoic acid, propyl ester p-Hydroxybenzoic acid, propyl ester p-Hydroxypropyl benzoate Propyl 4-hydroxybenzoate n-Propyl p-hydroxybenzoate Propyl p-hydroxybenzoate Propyl parahydroxybenzoate Propyl parasept Classification Organic ester Definition Ester of n-propyl alcohol and p-hydroxybenzoic acid Empirical C10H12O3... 

Alkyl esters (methyl, ethyl, propyl and heptyl esters, previously also benzyl ester) of p-hydroxybenzoic (4-hydroxybenzoic) acid are... 

Esters of 3,4 -tri-hydroxybenzoic acid R = C3H7 (Propyl) ss CgHp (Octyl)... 

As p-hydroxybenzoic acid esters present a relatively high pKa value (approx. 8.5), their antimicrobial action is less dependent on the pH value of the type of food to be preserved. In this respect they are superior to the organic preservative acids. Unfavourably, as in the case of phenol, p-hydroxybenzoic acid esters may be linked to some extent to proteins, emulsifiers or other food components on account of their phenolic hydroxylic-group and thus be inactivated. The antimicrobial action of the p-hydroxybenzoic acid esters is proportional to the alkyl chain length. Thus the antimicrobial action of the methyl ester is some 3 to 4 times, that of the ethyl ester some 5 to 8 times, that of the propyl ester about 25 times as powerful as phenol (Thompson, 1994). However, superimposed on this effect may be the water solubility of the esters, which is inversely proportional to the alkyl chain length. Since the activity spectra of the individual p-hydroxybenzoic acid esters are different, the application of mixtures can be profitable. 

Although the esters of />-hydroxybenzoic acid are not directly determinable by the 4-aminophenazone method (see p. 514) they can easily be converted to the acid by a preliminary hydrolysis and the general method can then be applied. Johnson and Savidge have found the following procedure to be satisfactory for the determination of methyl and propyl /)-hydroxybenzoates in a number of preparations. 

C12 to C20, primarily Ci6 to ( is), used as surface lubricants in the manufacture of food-contact articles. The method, which uses ethyl palmitate (Eastman Chemicals No. 1575 Red Label) as an internal standard, has been validated at 200 ppm total FAME [185]. Other FAME standards (methyl palmitate, methyl stearate, methyl oleate, methyl linoleate and methyl linolenate) are available (Applied Science Laboratories) [116], Worked out examples of additive determinations are given in the Food Additives Analytical Manual [116], which also describes a great many of indirect food additives, such as BHA, BHT, TBHQ, l-chloro-2-propanol, DLTDP, fatty acid methyl esters, w-heptyl-p-hydroxybenzoate, propyl-gallate, sodium benzoate, sodium stearoyl-2-lactylate, sorbitol and phenolic antioxidants. EPA methods 606 and 8060 describe the CGC separation of phthalate esters (direct injection) (cf. Figure 4.2). 

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