4-acetoxybenzoic Acid Research Articles

New polymer syntheses: 34. Copoly(ester imide)s of 4-hydroxybenzoic acid and N-(4-carboxyphenyl)-4-hydroxyphthalimide

N-(4-Carboxyphenyl)-4-acetoxyphthalimide was prepared from 4-hydroxyphthalic acid, 4-aminobenzoic acid and acetic anhydride. From this monomer a new homopoly(ester imide) was prepared by thermal condensation at 350°C in an inert reaction medium. By condensation with 4-acetoxybenzoic acid at 350°C a series of copoly(ester imide)s with variable composition was prepared. Differential scanning calorimetry measurements indicated a reversible first-order phase transition at temperatures between 340 and 390°C. Wide-angle X-ray scattering measurements revealed that the orthorhombic modification II (known from pure poly(4-hydroxybenzoate)) is predominant at low temperatures, whereas at high temperature a pseudohexagonal chain packing (modification III) is preferred. The isomeric copoly(ester imide)s derived from trimellitic anhydride, 4-aminophenol and 4-hydroxybenzoic acid possess quite different properties. The pseudohexagonal chain packing is adopted even at room temperature, and thus no phase transition occurs upon heating.

Synthesis of Segmented Anisotropic-Isotropic Poly(Aryl Ester)Poly(Arylene Ether) Copolymers

AbstractCarboxyl functional poly(arylene ether) oligomers of controlled number average molecular weight were synthesized via nucleophilic aromatic substitution step polymerization using p-hydroxy benzoic acid as the molecular weight and end group controlling reagents. The subsequent functionalized polyarylene ethers were copolymerized with acetoxy benzoic acid or acetoxyphenoxy benzoic acid via melt acidolysis procedures. Successful copolymers were generated using chlorobenzene as a solvent for the first s age of the reaction followed by melt reaction at temperatures as high as 325°C. Resulting copolymer composition and segment size were investigated. It was possible to prepare improved solvent resistant copolymers through incorporation of the liquid crystal polyester (LCP) segment. Extraction tests using boiling chloroform showed that a high percentage of segmented copolymer were generated. Swelling characteristics were also noted and were observed to decrease as a function of the LCP concentration utilized. Multiple transitions were observed in differential scanning calorimetry consistent with Tg's, Tm's and possibly with liquid crystal transitions. Optical microscopy showed an ordered microstructure developed which is consistent with the presence of liquid crystalline phases. The materials were successfully compression molded to afford tough coherent films at all compositions, implying the likelihood of improved compressive strength relative to the LCP homo- or copolyesters.

Topotactic transitions of the tetramer of P‐acetoxybenzoic acid

AbstractThermal and electron diffraction studies of single crystals derived from the tetramer of p‐acetoxybenzoic acid have revealed the presence of two consecutive crystallographic transformations, i.e., topotactic transitions. Thus, differential scanning calorimetry of the oligomer indicated two irreversible phase transitions, an endotherm followed by an exotherm, between 150 and 180°C, in addition to the crystal‐to‐nematic transition at 260°C. Electron diffraction analysis further elucidated the transformation occurring during thermal treatment of the original oligomer. Hence it could be shown that the solution‐crystallized material (α form) underwent a solid–solid phase transition to the β modification at a temperature corresponding to the observed endotherm. This β form then converted to a more stable modification (β′ form) which represented a superlattice structure derived from the β modification.

Inhibiton effect of cationic micelles on the basic hydrolysis of aromatic esters

The basic hydrolysis of 4-acetoxybenzoic acid and 2-naphtyl-acetate have been studied in cationic micelles of N-cetyl-N,N,N-tri-methylaamonium bromide and hydroxide and the results compared with the ones obtained for the basic hydrolysis of acetylsalicylic acid and 3-acetoxy-2-naphtoic acid. The results can be explained with the pseudo-phase kinetic Model and the determined second order rate constants in micelles are also smaller than the second order rate constants in water.

New polymer syntheses: 10. Syntheses of high molecular weight poly(4-hydroxybenzoate)s by bulk condensations of 4-hydroxybenzoic acids

The condensation of 4-hydroxybenzoic acid by means of various carboxylic acid anhydrides, acid chlorides and diphenylcarbonate has been investigated. All condensations were conducted in ‘one-pot procedures’. The average degrees of polymerization ( DP ) were determined by means of 1H nuclear magnetic resonance (n.m.r.) spectroscopic end-group analyses. The bulk condensation of 4-hydroxybenzoic acid by means of acetic anhydride at temperatures between 320° and 350°C was found to be the simplest and least expensive procedure. Yields between 97 and 99% and DP up to 300 were obtained in this way. Bulk condensations of purified acetoxybenzoic acid or condensations of 4-hydroxybenzoic acid with acetic anhydride in an inert solvent gave similar yields and DP . Also, the bulk condensations of 3,5-dimethyl-4-hydroxybenzoic acid, 3-methoxy-4-hydroxybenzoic acid, 3-chloro-4-hydroxybenzoic acid, 3,5-dichloro-4-hydroxybenzoic acid and 3,5-dibromo-4-hydroxybenzoic acid by means of acetic anhydride gave yields above 90%. However, the DP 's varied greatly with the nature of the substituents. ‘One-pot procedures’ using a variety of phosphorus derivatives as condensing reagents did not yield pure polyesters. The differential scanning calorimetry (d.s.c.) curves of the substituted poly(4-hydroxybenzoate)s do not show any endotherm, although X-ray diffraction measurements indicate a high degree of crystallinity. The thermogravimetric analyses demonstrate that the thermal stability depends largely on the synthetic procedure.

Synthesis and structure of the p‐hydroxybenzoic acid polymer

AbstractThe synthesis and structure of the p‐hydroxybenzoic acid polymer is described. The polymer was successfully prepared from either the phenyl ester of p‐hydroxybenzoic acid or from p‐acetoxybenzoic acid. With highly purified acetoxybenzoic acid, single crystals of the polymer could be prepared. The structure of the polymer was determined and shown to consist of a double helix where the two chains are in a reversed head‐to‐tail order. The unit cell dimensions are: a = 17.8 Å and c = 18.4 Å, where c corresponds to the chain length with a repeat distance of three units. The mechanism of polymerization and formation of the single crystal is discussed. The polymer displays a reversible high‐temperature crystalline transition at 325–360°C (not a melting point). The transition was characterized by differential thermal analysis, differential calorimetry, thermal expansion coefficient measurements, high‐temperature x‐ray scans, and dielectric constant determinations. Orientation of the polymer chains during fabrication and changes in the mechanism of oxidative degradation above the crystal transition are described.

The effects of some salicylate analogues on human blood platelets: 1. Structure activity relationships and the inhibition of platelet aggregation

Utilizing a turbidometric technique and human platelet-rich plasma (PRP) at 37°C, aspirin, 2-propionyloxybenzoic acid, 2,3-diacetoxybenzoic acid, sodium salicylate and 4-aminosalicylic acid, at suitable final concentrations and without prior incubation in PRP, prevented adenosine diphosphate (ADP)-induced second phase platelet aggregation and inhibited collagen-induced aggregation. The minimum concentrations of the latter four compounds which inhibited second-phase ADP aggregation were respectively, 15, 43, 60 and 100 times the minimum inhibitory concentration of aspirin. Without prior incubation, 2,6-diacetoxybenzoic acid and 3-propionyloxybenzoic acid potentiated the second phase of ADP aggregation while 3-acetoxybenzoic acid, 4-acetoxybenzoic acid and 2,4-diacetoxybenzoic acid had no effects. Aspirin, 2,3-diacetoxybenzoic acid, 2,6-diacetoxybenzoic acid and 2-propionyloxybenzoic acid, incubated in PRP at 37°C for 5 and 10 min, inhibited collagen-induced platelet aggregation in a concentration dependent manner. Aspirin was most potent, followed by 2-propionyloxybenzoic acid, 2,3-diacetoxybenzoic acid and 2,6-diacetoxybenzoic acid. Inhibition increased with the time of incubation in all cases. The results indicate that structural specificity (the presence of an acyl group in the 2 position of the benzene ring) is important for the aggregation inhibiting activity of aspirin, but do not support the contention that such inhibition is dependent upon the availability of an acetyl radical.