Polymers alcohol oxidation

Oxidation of LLDPE starts at temperatures above 150°C. This reaction produces hydroxyl and carboxyl groups in polymer molecules as well as low molecular weight compounds such as water, aldehydes, ketones, and alcohols. Oxidation reactions can occur during LLDPE pelletization and processing to protect molten resins from oxygen attack during these operations, antioxidants (radical inhibitors) must be used. These antioxidants (qv) are added to LLDPE resins in concentrations of 0.1—0.5 wt %, and maybe naphthyl amines or phenylenediamines, substituted phenols, quinones, and alkyl phosphites (4), although inhibitors based on hindered phenols are preferred. 

H. Hamamoto, M. Kudoh, H. Takahashi, H. Natsugari, S. Ikegami, Polyaerylamide-based Functional Polymer-Immobalized Perruthenate for Aerobic Alcohol Oxidation, Chem. Lett. 36 (2007) 632-633. 

Transition metal compounds, such as organic macrocycles, are known to be good electrocatalysts for oxygen reduction. Furthermore, they are inactive for alcohol oxidation. Different phthalocyanines and porphyrins of iron and cobalt were thus dispersed in an electron-conducting polymer (polyaniline, polypyrrole) acting as a conducting matrix, either in the form of a tetrasulfonated counter anion or linked to... 

Several other polymer-bound oxidizing reagents have recently been reported in the literature (reaction 14). A polyethyleneimine-supported silver dichromate 35 has been shown to be a stable, mild, and efficient oxidizing agent for the conversion of alcohols to carbonyl compounds.51 A... 

Methylpropene can be removed from the reaction mixture by distillation and easily is made the principal product by appropriate adjustment of the reaction conditions. If the 2-methylpropene is not removed as it is formed, polymer and oxidation products become important. Sulfuric acid often is an unduly strenuous reagent for dehydration of tertiary alcohols. Potassium hydrogen sulfate, copper sulfate, iodine, phosphoric acid, or phosphorus pentoxide may give better results by causing less polymerization and less oxidative degradation which, with sulfuric acid, results in the formation of sulfur dioxide. 

Apart from sodium hypochlorite, a number of alternative secondary oxidants for TEMPO-mediated alcohol oxidations can be employed. These include cerium (IV) ammonium nitrate (CAN),24 trichloroisocyanuric acid (TCCA),25 oxone ,26 MCPBA,2,3,7 PhI(OAc)2,27 W-chlorosuccinimide,28 sodium bromite,29 electrooxidation,8,21 H5IO626 and a polymer-attached diacetoxybromide (I) complex.30... 

Biffis et al. compared the catalytic performance of polymer gel immobilized Au NPs and Au/AC, with similar sized Au NPs, for alcohol oxidations in water [172]. Gold stabilized by polymer gel is advantageous over Au/AC for the use of hydrophobic substrates such as 1-octanol and 1-phenylethanol in aqueous media, although lower selectivity was obtained in some cases. For instance, polymer microgel supported Au NPs gave 1-octanoic acid by the oxidation of 1-octanol with a selectivity of 84% at 59% conversion, whereas Au/AC gave a selectivity of 93% at 65% conversion. 

In summary, the polymer-bound oxoammonium reagent was highly efficient in polymer-supported oxidations of various alcohols and was capable of cleanly converting chemically diverse compound collections. No overoxidation to carboxylic acids was observed. It is obvious that this reagent shall be of great value in polymer-supported transformations in solution, in automated parallel synthesis operations, and in flow-through reactors in up-scaled production processes. 

Fig. 6. Polymer-supported IBX (resin 5) can be activated and recycled with monoperoxy sulfonic acid (Caro s acid). The polymer reagent is capable of alcohol oxidations, dehydrogenations, and radical cyclization reactions.

Interestingly, the same reaction can be performed with the polymer-supported reagent 18 in water, because the reagent 18 was found to be considerably stable in this solvent. A mechanistic rationale of the catalytic activation of iodosobenzene 5 by potassium bromide is given in Scheme 14. This reaction provides a very facile and environmentally benign method for the alcohol oxidation. 

Here we report the use of a readily prepared polymer immobilised TEMPO as a catalyst for alcohol oxidations.15 It was derived from a commercially available oligomeric, sterically hindered amine, poly[[6-[(l,l,3,3-tetramethylbutyl)amino]-l,3,5-triazine-2,4-diyl] [2,2,6,6-teramethyl-4-piperidinyl)-imino]-1,6-hexane-diyl[(2,2,6,6-tetramethyl-4-piperidinylimino]], better known as Chimassorb 944 (MW 3000 see figure 3 for structure). This compound is used as an antioxidant and a light stabiliser for plastics. It contributes significantly to the long-term heat stability of polyolefins and has broad approval for use in polyolefin food packaging.16... 

Tsunoyama H, Sakurai H, Negishi Y, Tsukuda T (2005) Size-specific catalytic activity of polymer-stabilized gold nanoclusters in aerobic alcohol oxidation in water. J Am Chem Soc 127 9374-9375... 

Oxidation of a phenol to the corresponding ju-qninone nsing a copper catalyst takes place at room temperatnre nnder similar conditions as those nsed for alcohol oxidation, with O2 as oxidant. Likewise, hydroqninones (22) can be transformed to 3-alkoxy-/7-qninones (23) when reacted in the presence of an alcohol. In the case of 4-substituted phenols (24), polymer-based catalysts composed of ligands (e.g. PVBPy) that chelate copper have been used at elevated temperatures to selectively oxidize a benzylic carbon to yield 4-hydroxybenzaldehydes (25) in good yields. ... 

Another option is the use of both solid-supported versions of the catalyst and the co-oxidant. The Toy group in Hong-Kong has developed a multipolymer system for the TEMPO-catalyzed alcohol oxidation in which both the pre-catalyst and the co-oxidant are attached to a polymer. As it was clearly impossible to use two insoluble supported reagents, the idea was to use an insoluble polymer in conjunction with a soluble one. An insoluble polymer-supported diacetoxyiodosobenzene (PSDIB), an analog of 10, and a soluble polymer-supported TEMPO were used,... 

Scheme 10.19 Non-chiral polymer-supported oxidation catalysts and the use of one them in the direct oxidation of alcohols to a-tosyloxyketones (115).

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