Acetyl substitution patterns of amylose and amylopectin populations in cowpea starch modified with acetic anhydride and vinyl acetate

A comparative study on the acetylation of wood by reaction with vinyl acetate and acetic anhydride

Between 721.7 and 636.4 K, vinyl acetate undergoes thermal decomposition according to the rate equation log (k/s–1)= 10.43 – 182.4/2.303 RT(R= 8.312 J mol–1 K–1). Approximately 95% of reaction is decarbonylation to give acetone, with decomposition to ketene and acetaldehyde being the minor component. The latter reaction is an analogue of acetic anhydride pyrolysis which takes place at least 106 times faster per β-hydrogen at 600 K. This very large rate difference parallels that between β-keto-acids and βγ-alkenoic acids and contrasts markedly with pyrolysis of alkyl acetates and alkyl vinyl ethers, which occurs at closely similar rates. The contrasting behaviour most probably reflects differences in the principal bond-breaking step of the reaction, which for vinyl acetate and acetic anhydride (and also the acids) is breaking of the β–X–H bond so that the nucleophilicity of the attacking group assumes major importance; for esters and vinyl ethers this is not the most important step so their reaction rates are similar. The relative reactivities to the acids support an alternative view that both vinyl acetate and acetic anhydride pyrolyse via their enol forms. The greater understanding of the factors affecting gas-phase elimination rates permits prediction of the relative rates of compounds not yet studied. Pyrolysis of 1,2-diacetoxyethane gave non-first-order plots, with rate acceleration due to formation of the more reactive vinyl acetate. The β-acetoxy-group (OCOMe) increased the rate of elimination (per β-hydrogen at 600 K)ca. 7-fold, which compares with factors of 388 and 144 for COMe and CO2Me respectively, and a reduction of 3.6-fold by OMe.

In this study, the reactivity of wood components with acetic anhydride or vinyl acetate was studied. It was found that the reactivity of wood components was virgin wood flour > holocellulose >> a-cellulose. Acetylation of Turkish pine or cedar wood flour with acetic anhydride was significantly improved in the presence of potassium carbonate at 100°C. Maximum of about 20 and 18% weight percentage gain (WPG) values were obtained with Turkish pine ( Pinus brutia ) and cedar ( Cedrus libani ) wood flour after 3 h reaction at 100°C, respectively. The two modification methods and the effect of wood components on vinyl acetate (VA) or acetic anhydride (AA) modification, were characterised by infrared analysis in detail. As an apparent advantage of this new method, acetaldehyde was formed as by-product which is non-acidic was removed easily after the reaction due to low the boiling point of acetaldehyde [b.p. (760 mm Hg) = 21°C]. Key words : Acetic anhydride, vinyl acetate, holocellulose, α-cellulose, FTIR, chemical modification

Chemical modifications of Scots pine (Pinus sylvestris) wood flour were performed with vinyl acetate (VA) and acetic anhydride (AA) in the presence of potassium carbonate as a catalyst. Scots pine wood flour samples were successfully acetylated with VA (19 wt% gain) and AA (24 wt% gain). The effect of chemical modification of the Scots pine wood flour with AA and VA on the mechanical properties of wood high-density polyethylene composites (WPC) was determined. It was observed that acetylation of wood flour allowed a significant increase in both the mechanical properties and the thermal stability of the WPCs. It was concluded that acetylation of lignocellulosic fibers improves thermal stability, dispersion in the polymer matrix, and compatibility with the polymer matrix.

Comparative determination of the grafting distribution and viscoelastic properties of wood blocks acetylated by vinyl acetate or acetic anhydride

Acetic anhydride and vinyl acetate differentially modify the supramolecular structure of starch.

In-vitro and In-silico study on the acylation reaction of (-)-isopulegol and l-menthol with lipase from Rhizomucor miehei have been done. In this study, the acylation reaction was conducted by using two kinds of acyl source, acetic anhydride and vinyl acetate. The reaction was performed at 50°C and mole ratio of (-)-isopulegol:l-menthol:acetic acid anhydride or vinyl acetate was 1:1:3. In-vitro study, shows that lipase from Rhizomucor miehei have catalyzed the acylation reaction in a good way, whereas acetic anhydride was more effectively as acyl source than vinyl acetate. The selectivity product of (-)-isopulegyl acetate and l-menthyl acetate after reaction in 24 h are 34,58% and 21,52% respectively. In-silico study gives the results which correlated with in-vitro study, in case of determination the suitable of acyl source. There are verified by the value of Kd which represent the interaction between (-)-isopulegol, l-menthol or acyl source as ligand with lipase as macromolecule. This work also gives the prediction of mechanism reaction model from in-silico study

The chemical modification of wood has been the subject of research for many decades. The most favoured modification reaction involves the acetylation of wood with acetic anhydride. Reacted acetate provides dimensional stability by bulking the cell wall polymers and reduces further swelling when the woods come into contact with water. In addition that chemical modification also provides biological resistance. With acetylation, it is possible to extend at least twice or three times service life of wood as compared to control one. Acetylation of wood with acetic anhydride is not subjected to only academic studies, but also has become commercial process since 2003. The purpose of this study is to show the new methods for acetylation of wood. Turkish pine (Pinus brutia) sapwood was successfully acetylated by the new transesterification reaction with vinyl acetate. Under identical conditions, Turkish pine sapwood was also modified with acetic anhydride to compare with the new technique. The results of acetylated wood with acetic anhydride and vinyl acetate were compared, and characterized by Infrared (FTIR) and 13C cross polarisation-magic angle spinning nuclear magnetic resonance (CP MAS NMR) analysis. Key words: Acetylation, acetic anhydride, vinyl acetate, Turkish pine, chemical modification. .

Underutilized starch sources are gaining increasing recognition. However, the inherent functional deficiencies of native starch have limited its application in food industry. To counteract the deficiencies in its native characteristics, starch can be modified by acetylation. Two waxy starches (proso millet and amaranth) and four non-waxy starches (foxtail millet, quinoa, buckwheat, and oat) were modified by acetic anhydride and vinyl acetate, respectively. Degree of substitution of acetylated starches revealed that granule size did not significantly affect acetylation efficiency in starches from different plant origins. Acetylation increased peak and final viscosity of starches, with vinyl acetate exhibiting a more pronounced effect than acetic anhydride. Acetic anhydride decreased K and increased n values of non-waxy starches, showing reduced thickening ability. In contrast, vinyl acetate modification showed opposite trends, suggesting increased viscosity and pseudoplasticity. For non-waxy starches, G'25°C, G'0.1Hz, G'20Hz and gel hardness decreased after acetylation, indicating that acetylation contributed to a less solid and less elastic gel network. The extent of change in vinyl acetate modification was more pronounced than that of acetic anhydride. For waxy starch, vinyl acetate modification decreased tan δ25°C and increased gel hardness. In summary, acetylation reagent type was the major factor determining the pasting properties of acetylated starch, but the presence or absence of amylose would influence the rheological and gel properties of acetic anhydride and vinyl acetate modified starches. These findings could help unlock the potential applications of acetylated underutilized starches in the food industry.

Distribution of acetyl groups alters the properties of acetylated starch.

The products formed from the reactions of OH radicals with vinyl acetate and allyl acetate have been studied in a 1080 L quartz-glass chamber in the presence and absence of NO(x) using in situ FTIR spectroscopy to monitor the reactant decay and product formation. The yields of the primary products formed in the reaction of OH with vinyl acetate were: formic acetic anhydride (84 ± 11)%; acetic acid (18 ± 3)% and formaldehyde (99 ± 15)% in the presence of NO(x) and formic acetic anhydride (28 ± 5)%; acetic acid (87 ± 12)% and formaldehyde (52 ± 8)% in the absence of NO(x). For the reaction of OH with allyl acetate the yields of the identified products were: acetoxyacetaldehyde (96 ± 15)% and formaldehyde (90 ± 12)% in the presence of NO(x) and acetoxyacetaldehyde (26 ± 4)% and formaldehyde (12 ± 3)% in the absence of NO(x). The present results indicate that in the absence of NO(x) the main fate of the 1,2-hydroxyalkoxy radicals formed after addition of OH to the double bond in the compounds is, in the case of vinyl acetate, an α-ester rearrangement to produce acetic acid and CH(2)(OH)CO(•) radicals and in the case of allyl acetate reaction of the radical with O(2) to form acetic acid 3-hydroxy-2-oxo-propyl ester (CH(3)C(O)OCH(2)C(O)CH(2)OH). In contrast, in the presence of NO(x) the main reaction pathway for the 1,2-hydroxyalkoxy radicals is decomposition. The results are compared with the available literature data and implications for the atmospheric chemistry of vinyl and allyl acetate are assessed.

Characterization of differently sized granule fractions of yellow pea, cowpea and chickpea starches after modification with acetic anhydride and vinyl acetate

Starches were isolated in 36, 37 and 28% yields, from chick pea, cow pea and horse gram, respectively. Study of their properties revealed mixed granule population; single stage swelling with high solubility in water for cow pea and horse gram starches in comparison to chick pea starch; slightly higher solubility in DMSO for chick pea starch followed by cow pea and horse gram starches; a relatively high viscosity in alkaline solution of cow pea starch; and Brabender amylograms indicating a low slurry viscosity and low set back in the case of chick pea starch compared to the other two starches which exhibited considerable peak viscosity as well as retrogradation. All the starches contained amylose in the range of 32 – 34%. X‐ray powder patterns showed chick pea and horse gram starches to be of B‐type, whereas cow pea starch was of A‐type.

The performance of two native lipases (lipase from Aspergillus niger and Rhizoupus oligosporus) in the resolution of (RS)-phenylethylamine (1), varying the temperature, acyl donor type (ethyl acetate, vinyl acetate, iso-propenyl acetate and acetic anhydride) and organic medium, was studied. The effect of the nature of the anion using native A. niger lipase in n-heptane with a series of imidazolium-based ILs [BMIm][X], where X = BF4, PF6, SCN and Cl, was also evaluated. Using the lipase from A. niger, the R-2b amide was obtained with conversions from 6 to > 99% and E-values from 2 to > 200, with n-heptane or n-hexane. This lipase showed better E-values in a two-phase system using n-heptane and [BMIm][PF6] or [BMIm][BF4] 9:1 (v/v), obtaining values of 9 and 7, respectively, when vinyl acetate was used as the acyl donor, compared to the use of pure n-heptane (E = 2). The series for the anions in terms of decreasing performance was as follows: PF6- >BF4- > SCN- > Cl-.

The purpose of this study was to compare two different acetylation mechanisms using acetic anhydride (AA) or vinyl acetate (VA) modification with using various catalysts. Acetylation of Scots pine wood flour with acetic anhydride could be significantly improved in the presence of potassium acetate, potassium carbonate, and sodium carbonate at 100°C. Sodium carbonate had low effect on VA acetylation, potassium acetate was found to be more effective, and potassium carbonate was better for vinyl acetate modification of wood flour. The two modification methods and the effect of different catalysts on AA or VA modification were characterized by infrared and NMR spectra and analyzed in detail. The acetylation of Scots pine flour with VA and AA showed almost the same WPG values for catalysts when based on long reaction times.