Benzylation of Peat by a Mechanochemical Method
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BENZYLATION OF PEAT BY A MECHANOCHEMICAL METHOD
M. V. Efanov,1,2* M. P. Sartakov,1,2 and V. V. Kon′shin2
Research on chemical modification of wood, which is a source of renewable feedstock [1], has grown in the last decades. Thermoplastic cellulose-containing polymers that can be used as binders for composites are highly interesting in technology. Cellulose and cellulose-containing materials cannot be heat treated because extensive thermal degradation occurs before its melting point, i.e., cellulose has very high cohesive energy because of intra- and intermolecular H-bonds so that the melting point of cellulose is higher than its degradation threshold. Thermoplasticity can be achieved only by reducing the degree of hydrogen bonding by chemically altering the hydroxyls. Cellulose-containing materials can be converted to a thermoplastic state by introducing nonpolar substituents, e.g., benzyl and others [2]. Several processes for producing thermoplastic benzyl-woods [3] and acetyl-woods, mixed wood esters, and other lignocarbohydrate materials [4] have been reported. However, benzylation of peat has not been reported in the literature. Katrakov et al. showed that wood could in principle be benzylated by benzylchloride in the presence of NaOH by a mechanochemical method [5]. Peat contains cellulose, lignin, hemicellulose, and humic substances that have hydroxyls of different reactivities that can be O-alkylated by benzylchloride in basic solution. The goal of the present work was to study peat benzylation using benzylchloride in the presence of NaOH by a mechanochemical method. The process for benzylation of the OH groups of plant feedstock was based on the usual Williamson reaction (O-alkylation) R–OH + C6H5CH2Cl + NaOH = R–O–CH2–C6H5 + NaCl + H2O. The theoretically maximum composition could contain 42.2% bound benzyl groups according to the total content of OH groups (13.6%, 0.008 mol/g of peat) in the starting peat and the analogous equation for benzyl wood esters [6]: COH(BG) = (17C/91)/(1-91C/9100), %, where COH(BG) is the number of reacted OH groups (%); C, content of bound benzyl groups (%); 17, molecular weight of OH; 91, molecular weight of benzyl. Thus, the degree of conversion of OH groups by the benzylation ( α, %) could be determined from the ratio of the experimentally determined content of bound benzyl groups added to the peat to the theoretically possible content. The effect of the peat mechanochemical activation time by benzylchloride in the presence of NaOH with an OH–NaOH mole ratio was studied. The content of bound benzyl groups and solubility of the obtained products in Me2CO and CHCl3 increased smoothly as the time of alkaline mechanochemical activation of the peat increased from 10 to 60 min with equimolar amounts of base and alkylating agent (Table 1). The IR spectrum of the maximally benzylated product (Table 1) contained a triplet of CAr–H stretching vibrations in the range 3030–3090 cm–1, a strong absorption band at 2900–2950 cm–1 for benzyl CH2 stretching vibrations, and aromatic absorpti
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