Surface Esterification

A partly hydrophobic and organophilic silica can be made very simply by a process patented by Goebel (507b). Fine silica powder is dehydrated and the surface dehydroxylated to an optimum degree by heating it for 1.5 hr in air at 470-530 C. The BET area was 297 m g but the resulting specific hydroxylated area was 184 m g . When this powder was cooled and refluxed at 118 C in butanol at atmospheric pressure or even when simply exposed to butanol vapor in a closed container for a week, esterification occurred and the surface became about half covered with attached butoxy groups. 

The n-butoxy groups on the fully esterified surface are remarkably stable (samples 

A variety of ester groups have been explored, some of which were discussed in Chapter 4 in connection with organosols. There are many types of SiOR groups, such as where R is nitroalkyl, chioroalkyl, or alkoxyalkyl (508) R contains an acidic substituent such as mercapto, phenolic, sulfonic, phosphonic, or carbamic (509) R contains fluorocarbon groups, for example, OCHi(CF,) X, where X - H or F and n 1-17 (510) ORN and ORS, where N and S are in the form of onium ions 

Kitahara and Asano (518) investigated the silica-methanol system up to high temperatures and pressures and found up to 5 methoxy groups nm esterifled to the surface. They also made similar studies with higher alcohols. 

Pyrogenic silica can be given an esterifled surface by treatment with (C4H,0)4Si vapor at up to 300 C out of contact with air using some dry ammonia as catalyst (519). 

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Kinetic parameters of the surface esterification were determined from the analysis of surface OH groups and chemisorbed methoxy species concentrations during the reaction assuming that k i = k3 = 0 Ef — = 27.5 kj mole ki/k2 = 0.33 at 150°C and 0.64... 

D. Pasquini, M. N. Belgacem, A. Gandini, and A. A. D. Curvelo, Surface esterification of cellulose fibers Characterization by DRIFT and contact angle measurements, J. Colloid Interface Set, 295 (2006) 79-83. 

H. Yuan, Y. Nishiyama, and S. Kuga, Surface esterification of cellulose by vapor-phase treatment with trifluoroacetic anhydride, Cellulose, 12 (2005) 543-549. 

Berlioz S, Molina-Boisseau S, Nishiyama Y et al (2009) Gas-phase surface esterification of cellulose microfibrils and whiskers. Biomacromolecules 10 2144-2151 Bhatnagar A, Sain M (2005) Processing of cellulose nanofibre-reinforced composites. J Reinf Plast Compos 24 1259-1268... 

Sobkowicz MJ, Braun B, Dorgan JR. Decorating in green surface esterification of carbon and cellulosic nanoparticles. Green Chem 2009 1 680-682. 

X-ray diffractograms of (I) BzClSOH-modified clay and (11) clay of I after surface esterification reaction with dotriacontanoic acid. The peak at 8.84 29 corresponds to the 001 basal plane spacing of mica platelets used as the internal standard. (Reproduced from Mittal, V., Journal of Colloid and Interface Scimce, 315,135-41,2007. With permission from Elsevier.)... 

This work reports the use of benzophenone, a very well characterized probe, to study new hosts (i.e., modified cellidoses grafted with alkyl chains bearing 12 carbon atoms) by surface esterification. Laser-induced room temperature luminescence ofair-equilibrated or argon-purged solid powdered samples of benzophenone adsorbed onto the two modified celluloses, which will be named C12-1500 and Cl2-1700, revealed the existence of a vibrational-ly structured phosphorescence emission of benzaphenone in the case where ethanol was used for sample preparation, while a nonstructured emission of... 

Ethyl p-aminobenzoate (esterification of p-aminobenzoic acid). Place 80 ml. of absolute ethyl alcohol in a 250 ml. conical flask equipped with a two-holed cork and wash-bottle tubes. Pass dry hydrogen chloride (Section 11,48,2) through the alcohol until saturated—the increase in weight is about 20 g.—and transfer the solution to a 250 ml. round-bottomed flask. Introduce 12 g. of p-aminobenzoic acid, fit a double surface condenser to the flask, and reflux the mixture for 2 hours. Upon... 

Titanium alkoxides are used for the hardening and cross-linking of epoxy, siUcon, urea, melamine, and terephthalate resins in the manufacture of noncorrodable, high temperature lacquers in the sol-gel process as water repellents and adhesive agents (especially with foils) to improve glass surfaces as catalyst in olefin polymeri2ation, and for condensation and esterification. 

Sorbitol is the most important higher polyol used in direct esterification of fatty acids. Esters of sorbitans and sorbitans modified with ethylene oxide are extensively used as surface-active agents. Interesteritication of fatty acid methyl esters with sucrose yields biodegradable detergents, and with starch yields thermoplastic polymers (36). 

Cellulose activated with ethylenediarnine [107-15-3] is used to prepare high molecular-weight cellulose butyrate (23). Cellulose so activated has a larger measured surface area (120 m /g) than cellulose activated with acetic acid (4.8 m /g). The diamine is removed with water, followed by solvent exchange with acetic acid and butyric acid before esterification. 

The esterification of -butyl alcohol and oleic acid with a phenol—formaldehydesulfonic acid resin (similar to amberHte IR-100) is essentially second order after an initial slow period (52). The velocity constant is directiy proportional to the surface area of the catalyst per unit weight of reactants. 

In a micro reactor, there is much more surface available than in standard reactors [18]. Thus, surface-chemistry routes may dominate bulk-chemistry routes. In this context, it was found sometimes micro-reactor routes can omit the addition of costly homogeneous catalysts, since the surface now undertakes the action of the catalyst. This was demonstrated both at the examples of the Suzuki coupling and the esterification of pyrenyl-alkyl acids. 

In this context, the esterification of 4-(l-pyrenyl)butyric acid with an alcohol to the corresponding ester was investigated [171]. Without the presence of sulfuric acid no reaction to the ester was foimd in the micro reactor. On activating the surface by a sulfuric acid/hydrogen peroxide mixture, however, a yield of 9% was achieved after 40 min at 50 °C. On making the surface hydrophobic by exposure to octadecyltrichlorosilane, no product formation was observed. Using silica gel in a laboratory-scale batch experiment resulted in conversion, but substantially lower than in the case of the micro reactor. The yield was no higher than 15% (40 min ... 

Surface effects in the esterification of 9-pyrenebutyric acid within a glass micro reactor, Chem. Commun. (2003) 1924-1925. 

First investigations revealed a comparison of batch-scale performance with micro-channel processing [91]. Further investigations of the role of surface effects catalyzing the esterification concerned the deliberate enhancement in the number of silanol groups on the glass surface of such micro-channel reactors. 

The pore size of the catalyst plays an important role as the reactants and the products must be able to lit inside the catalyst to take full advantage of the total surface area available. The pore size of metal oxides are sufficiently large (>2 nm) to facihtate the mass transfer into and from the catalyst pores. This compensates for their lower acidity compared to other sohd acids. Table 33.1 gives an overview of the tested catalysts, showing their pros/cons with respect to the fatty acid esterification reaction. 

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