Combination etherification

Modifications in the production of biodiesel can result in valuable glycerol as a byproduct and in fewer separation steps. The modifications studied or considered include combining etherification of glycerol into the biodiesel production process, etherification in situ within the biodiesel process and a biodiesel process with heterogeneous catalyst. 

Several derivatives of cellulose, including cellulose acetate, can be prepared in solution in dimethylacetamide—lithium chloride (65). Reportedly, this combination does not react with the hydroxy groups, thus leaving them free for esterification or etherification reactions. In another homogeneous-solution method, cellulose is treated with dinitrogen tetroxide in DMF to form the soluble cellulose nitrite ester this is then ester-interchanged with acetic anhydride (66). With pyridine as the catalyst, this method yields cellulose acetate with DS < 2.0. 

Partial etherification of the beech wood MGX with p-carboxybenzyl bromide in aqueous alkali yielded fully water-soluble xylan ethers with DS up to 0.25 without significant depolymerization the Mw determined by sedimentation velocity was 27 000 g/mol [400,401]. By combination of endo- 6-xylanase digestion and various ID- and 2D-NMR techniques, the distribution of the substituents was suggested to be blockwise rather than uniform. The derivatives exhibited remarkable emulsifying and protein foam-stabilizing activi-... 

A trifold anionic/pericyclic domino reaction was used for the synthesis of the dioxapyrrolizidine 2-655 combining a nitro aldol condensation, SN-type cyclization, SN-type etherification, and an intramolecular 1,3-dipolar cyclization as described by Rosini and coworkers (Scheme 2.148) [339]. 

Two of the hydroxyl groups present in each glucose unit of the cellulose are secondary, one is primary. Studies on the relative rates of etherification of the three hydroxyls are not conclusive. Mahoney and Purves,18 using a method which takes advantage of the rapid reaction between tosyl chloride and a primary hydroxyl, combined with a determination of unsubstituted glycol groups, have studied the relative num-... 

Etherification using a metal vinylidene has also been combined with G-G bond formation through the reaction of an alkynyl tungsten complex with benzaldehyde (Scheme 14). The addition of an internal alcohol to the incipient /3,/Udialkylvinylidene that is generated leads to dehydration and the formation of a Fischer-type alkylidene complex. Further reactions of this carbene with a range of nucleophiles have provided access to various furan derivatives.374,375... 

Catalysts lacking phosphorus ligands have also been used as catalysts for allylic substitutions. [lr(COD)Cl]2 itself, which contains a 7i-accepting diolefin ligand, catalyzes the alkylation of allylic acetates, but the formation of branched products was only favored when the substitution reaction was performed with branched allylic esters. Takemoto and coworkers later reported the etherification of branched allylic acetates and carbonates with oximes catalyzed by [lr(COD)Cl]2 without added ligand [47]. Finally, as discussed in Sect. 6, Carreira reported kinetic resolutions of branched allylic carbonates from reactions of phenol catalyzed by the combination of [lr(COE)2Cl]2 and a chiral diene ligand [48]. 

Hartwig et al. demonstrated that the same combination of iridium precursor and phosphoramidite LI also catalyzes allylic etherifications (Scheme 9) [68]. Lithium and sodium aryloxides were shown to react with cinnamyl and hex-2-enyl carbonates to form the branched allylic ethers in high yield, with high branched-to-linear... 

Although the combination of [Ir(COD)Cl]2 and LI was shown to catalyze the alkylation, amination, and etherification of allyiic esters to form the branched substitution product in high yield and enantioselectivity, the identity of the active catalyst in these reactions had not been identified. The combination of [Ir(COD) Cl]2 and LI forms the square-planar [Ir(COD)(Cl)Ll] (4) (Scheme 11) [45]. However, this complex does not react with allyiic carbonates to form an appreciable amount of an aUyl complex, and the absence of this reactivity suggested that the mechanism or identity of the active catalyst was more complex than that from simple addition of the allyiic ester to the square-planar complex containing a k -phosphoramidite ligand. 

Although the Ir-catalyzed aUyhc substitution was developed only recently, several applications in the areas of medicinal and natural products chemistry have aheady been reported. In many syntheses the allylic substitution has been combined with a RCM reaction [71]. Examples not directed at natural products targets have aheady been described in Sections 9.4 and 9.5. It has also been mentioned that this strategy had previously been used in conjunction with aUyhc substitutions catalyzed by other transition metals (Figure 9.5). This was pioneered by P. A. Evans and colleagues, who used Rh-catalyzed allylic amination (compound A in Figure 9.5) [72] and etherification (compound B) [73], while Trost and coworkers demonstrated the power of this concept for Pd-catalyzed aUyhc alkylations (compound C) [74] and Alexakis et al. for Cu-catalyzed (compound D) aUyhc alkylations [75]. 

Dual modification Acetylated distarch phosphate - Esterification by sodium trimetaphosphate or phosphorus oxychloride combined with esterification by acetic anhydride or vinyl acetate Hydroxypropyl distarch phosphate - Esterification by sodium trimetaphosphate or phosphorus oxychloride combined with etherification by propylene oxide... 

Most of the matrices for aerospace composites are based on a combination of TGMDA and DDS and/or Dicy. Again reactions are very complex and different reaction paths could be considered additions, etherifications, but also cyclizations introduced by the neighboring N,N-diglyci-dyl groups ... 

The most important examples of reactive separation processes (RSPs) are reactive distillation (RD), reactive absorption (RA), and reactive extraction (RE). In RD, reaction and distillation take place within the same zone of a distillation column. Reactants are converted to products, with simultaneous separation of the products and recycling of unused reactants. The RD process can be efficient in both size and cost of capital equipment and in energy used to achieve a complete conversion of reactants. Since reactor costs are often less than 10% of the capital investment, the combination of a relatively cheap reactor with a distillation column offers great potential for overall savings. Among suitable RD processes are etherifications, nitrations, esterifications, transesterifications, condensations, and alcylations (2). 

The activity of the 4-alkylpyrocatechols (la), 3-alkylpyro-catechols (lb), 3,5-dialkylpyrocatechols (Ic), 3,6-dialkylpyro-catechols (II), 4,5-dialkylpyrocatechols (III), 3,4,6-trialkyl-pyrocatechol (TV), and 4,5- and 4,6-dialkyl-2-alkoxyphenols (V and VI) was studied in isotactic polypropylene at 180 =t 0.1° C. The relative activities Ar were correlated with substituent constants and redox potentials. In the la series the activity of 4-n-alkyl derivatives exceeded that of 4-tert-alkyl derivatives. The length of the main alkyl chain in la and lb and the steric effects in the latter exerted a specific favorable influence. In agreement with these effects, 3-tert-alkyl-5-methyl derivatives are the most active compounds in Series Ic compounds with other combinations of alkyls are weaker antioxidants as are the isomeric substances II and III or compound IV. Etherification of one hydroxyl group exerts an unfavorable effect influences of substitution in 2-alkoxyphenols (V and VI) are generally the same as in the pyrocatechols Z-ZZZ. 

Various chemical modifications of wood have been tried to improve native properties such as swelling and shrinking and to apply new properties such as thermoplasticity, solubility, and so on [1-5]. These treatments will increase the use of wood as an important renewable resource. Several kinds of treatments have been applied to cellulose alone, whose properties have been studied by many scientists [6-9], e.g., esterification, etherification, and cya-noethylation. As for wood, the introduced side chains with these reactions are combined with OH groups of its several components, especially those of cellulose chains. The treatments give new properties due to the introduced side chains and to the change of the conditions around the side chains, so that the interaction between wood components molecular main chains is remarkably varied. Thus, new physical and chemical properties are applied to wood with such chemical modifications. 

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