Ethyl acetate 4-hydroxybenzoic acid

C21H25O4 23637-81-2) see Gestrinone ethyl 4-hydroxybenzoic acid (QjHiqOj 120-47-8) see Gabexate ethyl (2-hydroxybenzylamino)acetate (C H,5N03 57938-78-0) -see Caroxazone... 

Phenolic acids. Table 11 lists the Rf values for a number of phenolic acids and certain of their relatives on silica gel, silanized silica gel, cellulose, and polyamide layers. Silica gel (Silica Rapid Platten Woelm F-254) was used with solvents I [dichloromethane-toluene-formic acid (50 40 10)] and II [dichloromethane-acetic acid-water (100 50 50, lower phase)], followed by UV examination of the plates and subsequent spraying with 1 % methanolic ferric chloride. HPTLC precoated plates with silica gel 60 F-254, RP-8, and Wang polyamide were used with solvents 111 [benzene-ethyl acetate-formic acid (40 10 5)], IV [ethanol-water (55 45)], and IX [benzene-ethyl methyl ketone-methanol (60 26 14)], respectively. The upper part of Table 11 lists the Revalues of hydroxybenzoic acids and the lower part those for hydroxycinnamic acids. For columns V, VI, VII, and VIII, the solvents used were 2% formic acid (V), 20% potassium chloride solution (VI), isopropanol- ammonium hydroxide-water (8 1 1) (VII), and 10% acetic acid (VIII). For each layer the relative trends of the Revalues follow the polarity of the compounds listed. Table 12 gives the Revalues for certain phenolic acids on silver oxide-impregnated silica gel G by two-dimensional development on cellulose (107). 

The influence of NH., and CO, on the chromatographic behaviour of benzoic acid and its derivatives (o-, m-, p-hydroxybenzoic, nitrobenzoic, aminobenzoic, chlorobenzoic acids) was studied. The work was carried out by means of upgoing TLC on Sorbfil plates. Isopropanol- and ethyl acetate-containing water-organic eluents were used as mobile phases in the absence or presence of gaseous modifiers in the MP. The novel modification of TLC has been found to separate benzoic acids with different values of their dissociation constants more effectively than water-organic mobile phases. 

The reference intermolecular reaction for the aliphatic compounds is the formation of ethyl acetate from ethanol and acetic acid measured under the same conditions (20% ethanol-water, ionic strength 0.4 M) by Storm and Koshland (1972a). The esterification of benzoic acid in methanol at 25° is 290 times slower than that of acetic acid (Kirby, 1972), so this factor is used to correct the EM s, calculated otherwise in the same way, for the hydroxybenzoic acids. For the phenolic acids see notes m and n b Rate constants are in units of dm3 mol-1 s-1 c Storm and Koshland, 1972a d Storm and Koshland, 1972b Bunnett and Hauser, 1965... 

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. 

Flak and Schaber (5,62) used reverse-phase HPLC for the quantitative and simultaneous determination of benzoic acid and sorbic acid, as well as 4-hydroxybenzoic acid, salicylic, 5-nitrofurylacrylic, and p-chlorobenzoic acid and the EsHBA (methyl, ethyl, propyl) in wines and beverages. The first five compounds can be determined by isocratic elution from a Clg column using 0.12 M acetate, pH 3.8 acetonitrile (85 15), and all may be separated with gradient elution (increasing acetonitrile from 10 to 60%, with a simultaneous decrease of the pH of the acetate buffer from 3.9 initially to 3.3). 

Rump [17] has described a cellulose thin layer method for the detection of phenolic acids such as iw-hydroxybenzoic acid, iw-hydroxyphenylacetic acid and m-hydroxyphenylpropionic acid, in water samples suspected to be contaminated with liquid manure. The phenolic acid is extracted with ethyl acetate from a volume of acidified sample equalling lmg of oxygen consumed (measured with potassium permanganate). The ethyl acetate is evaporated and the residue dissolved in ethanol. After spotting of a lpm aliquot on a cellulose plate the chromatogram is developed by capillary ascent with the solvent n-propanol-w-butanol-25% NH3-water (4 4 1 1 by vol). The solvent front is allowed to advance 10cm. The air-dried plate is sprayed with a diazotised p-nitroanilinc reagent to make the phenolic acids visible. 

The ethyl ester of / -hydroxybenzoic acid was hydrogenated to give high yields of the saturated 4-hydroxy ester either over Pd-SrC03 in dioxane (see eq. 11.24)113 or ethyl acetate195 at 155-160°C, and over rhodium oxide at 50-65°C or over ruthenium oxide at 95-100°C in ethanol with small amounts of acetic acid (see eq. 11.25),114 under high hydrogen pressures. 

The present procedure affords 4-hydroxy[l-13C]benzoic acid from ethyl [2-13C]acetate in three steps with 72% overall yield. It is based on an observation of Woodward17 that ethyl 4-hydroxybenzoate is formed by base-catalyzed condensation of 4H-pyran-4-one with diethyl malonate. The submitters studied several solvent-base combinations for this reaction and found that tert-butyl alcohol/potassium tert-butoxide gave the highest yields. When a stoichiometric amount of the base is used, an excess of 4H-pyran-4-one has to be used.4 ) This can be avoided by the use of substoichio-metric amounts as given in the procedure. 

For the chlorination of ethyl /7-hydroxybenzoate by S02C12 see page 162. 3,5-Dibromo-4-hydroxybenzoic acid is readily available on addition of bromine (2 moles) in glacial acetic acid to /7-hydroxybenzoic acid in the same solvent, with final heating on a steam-bath. 

Phenolic acids (ferulic, syringic,/>-coumaric, vanillic, caffeic, protocatechuic, and p-hydroxybenzoic) were extracted fi-om soil and analyzed on a C g column X = 245 nm) using a 38-min 70/30 -> 30/70 (2/97.25/0.5/0.25 methanol/water/ acetic acid/ethyl acetate)/(80/17/2/1 methanol/water/acetic acid/ethyl acetate) gradient. Detection limits were reported as <1 pg/g for all compounds [113]. A working concentration curve of 1-lOpg/mL was also generated. 

Acetate ion Acetic acid Benzoic Acid Benzoic Acid Benzoic Acid Benzoic Acid Ethyl 4-hydroxybenzoate Ethyl salicylate Humic acid... 

As stated above, one of the routes to thienothiophene 2 is cyclization of (3-thienylthio)acetic acid in the presence of concentrated sulfuric acid followed by action of the 2,3-dihydrothieno[3,2-i]thiophen-3-one (22, R = H) formed with lithium aluminum hydride.26,28 Attempts by the present authors41,33 as well as those of Gronowitz and Moses47 to obtain thienothiophene 1 by cyclizing (2-thienylthio)acetic acid or its chloride by various catalysts (stannic chloride, aluminum chloride or bromide, polyphosphoric acid or anhydrous HF) were unsuccessful. Synthesis of 2-ethyl-3-hydroxythieno[2,3-A]thiophene33 by procedures commonly used for the preparation of 3-hydroxybenzo[A]thiophene72-74 also failed. 

A gas chromatographic method may be employed for analysis for both benzoic acid and sorbic acid in food, as described in AOAC method 983.16. The acids are extracted from an acidified aqueous homogenized food sample into ether. The acids are then extracted from the ether solution into aqueous alkali, and after acidification they are re-extracted into dichloromethane. Treatment of the residue with N-methyl-N-trimethylsilyltrifluoroacetamide converts the benzoic and sorbic acids into trimethylsilyl esters. These esters are then analyzed with a glass column packed with a support coated with OV-1, in a temperature programmed analysis. Phenylacetic and caproic acids are used as internal standards for benzoic and sorbic acids, respectively. An LC method has also been described for analysis of benzoic acid with simultaneous determination of sorbic acid, and methyl, ethyl, propyl, and butyl p-hydroxybenzoates. The preservatives were extracted from meat or seasonings with 70% ethanol, and analyzed by reversed-phase LC using a Cig stationary phase with a linear gradient from 10 to 70% methanol in 1.5% aqueous ammonium acetate and 1.5% aqueous acetic acid. 

Separation of methyl, ethyl and propyl p-hydroxybenzoates succeeds on rigorously dried, highly active silica gel 6F254 layers (3 h at 160° C) or by triple development with the solvent petrol ether-diethyl ether-acetic acid (81 + 5 + 14) [21]. 

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