Surface acetylation

Kiguchi, M. (1997). Photo-deterioration of chemically modified wood surfaces acetylated wood and alkylated wood. Japan Agricultural Research Quarterly, 31(2), 147-154. 

Tracer studies with 13C showed that the carbon of methoxy species formed in CO hydrogenation appeared as the central C atom of isobutylene.531 Methoxy was shown to be reduced to surface methyl species that was transformed to surface acetyl group via insertion of CO into the methyl-metal bond. Aldol condensation of C2 oxygenates with formaldehyde affords iso-C4 products.532 Earlier results of a different approach for isosynthesis using metal-zeolite catalyst systems are summarized in a 1998 review.533... 

Methane, acetic acid, acetaldehyde, and ethanol constitute approximately 90 carbon atom percent of the primary products from the hydrogenation of CO over Rh/SiO and Rhr-Mn/SiOi catalysts at 250 -300°C and 30-200 atm pressure in a back-mixed reactor with H /CO = 1. The rate of reaction and the ratio, CHj /C chemicals, vary with (Pjy / The addition of 1% Mn raises the synthesis rate of a 2.5% Rh/SiOfi catalyst about tenfold. The kinetics and the product distribution are consistent with a mechanism in which CO is adsorbed both associatively and dissodatively. The surface carbon produced by the dissociative CO chemisorption is hydrogenated through a Rh-CHs intermediate, and CO insertion in that intermediate results in formation of surface acetyl groups. 

Methyl acetate synthesis rate does not depend on DME pressure, but increases linearly with CO pressure up to 10 atm. This kinetic response is consistent with a sequence of elementary steps (Fig. 6) involving the formation of surface methyl groups at Brpnsted acid sites initially via direct DME reactions with protons and then via chain transfer reactions (propagation steps) of DME with surface acetyls formed via rate-determining CO insertion into C-0 bonds in methyl groups at the catal3rtic steady state (92). CO insertion occurs from the gas phase or via weakly held CO species adsorbed noncompetitively with CH3 groups. 

Lin N, Huang J, Chang PR, Feng JW, Yu JH. Surface acetylation of cellulose nanocrystal and its reinforcing function in poly(lactic acid). Carbohydr Polym 2011 83 1834-1842. 

Zini et al. [50] prepared composites of a bacterial copolyester poly(3-hydroxybutyrate-co-3-hydroxyhexanoate], P(3HB-co-3HH), reinforced with flax fibers by compression molding. In order to improve fiber-matrix adhesion in composites, fibers chemically modified at the surface (by acetylation or by short-chain-PEG grafting] were also used. The best results were obtained with surface acetylated fibers. In the flax fiber composites the crystallization rate of P(3HB-co-3HH] remarkably increased compared with that of the plain polyester. The fibers displayed a nucleating effect on P(3HB-co-3HH] crystallization, whose magnitude depended on fiber surface chemistry. This feature was confirmed by the appearance of trans-crystallinity in isothermal crystallization experiments run in a hot stage of a polarized optical microscope. 

KoLhatkar, R. B., Kitchens, K. M., Swaan, P. W., and Ghandehari, H. 2007. Surface acetylation of polyami-doamine (PAMAM) dendrimers decreases cytotoxicity while maintaining membrane permeability. Bioconjug Chem 18(6), 2054-2060. 

In a similar study by Kim et al. [34] heterogeneous surface acetylation of BC resulted in DS values between 0.04 and 2.77, as determined by titration and FT-IR. The D S could be controlled by changing the amount of acetic anhydride added. X-ray diffraction showed that the acetylation proceeded from the surface of the microfibrUs, leaving the core portion unreacted. SEM analysis revealed that even low levels of acetylation effectively prevented aggregation of the microfibrils on direct drying from water, as a result of an increase in surface hydrophobicity. Yamamoto et al. [39] have reported CP/MAS NMR spectroscopic studies of the effects of solid-phase acetylation on BC structure. The DS ranged from 1.19 to 2.73. Like Kim et al, they found evidence that acetylation proceeded from the surface to the core of each microfibril. 

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