Phenyl ether bond linkages

In addition to ester-linkages, hydroxycinnamic acids can also be covalently linked to cell wall components via phenyl ether bonds. While this has only been demonstrated for wheat (Triticum aestivum L.) straw lignin... 

In addition to sulfone, phenyl units, and ether moieties, the main backbone of polysulfones can contain a number of other connecting units. The most notable such connecting group is the isopropylidene linkage which is part of the repeat unit of the well-known bisphenol A-based polysulfone. It is difficult to clearly describe the chemical makeup of polysulfones without reference to the chemistry used to synthesize them. There are several routes for the synthesis of polysulfones, but the one which has proved to be most practical and versatile over the years is by aromatic nucleophilic substitution. This polycondensation route is based on reaction of essentially equimolar quantities of 4,4,-dihalodiphenylsulfone (usually dichlorodiphenylsulfone (DCDPS)) with a bisphenol in the presence of base thereby forming the aromatic ether bonds and eliminating an alkali salt as a by-product. This route is employed almost exclusively for the manufacture of polysulfones on a commercial scale. 

These three monomers are linked together by enzymatic dehydrogenation via phenoxy radicals into a three-dimensional irregular polymer network with C-C and C-O-C linkages. One third of the phenyl-propane units are linked by carbon-carbon bonds, two thirds by ether bonds. Lignins of different origin differ in their structure. 

The butynyl(phenyl)iodonium triflates 243, possessing an ether or acetal linkage at C-4, react with sodium />-toluenesulfinate to give the 3-tosyldihydrofurans 244 (00OL2603, OOJOC8659). These formal carbenic C-O bond insertions are thought to occur through vinyloxonium ylide intermediates (Scheme 67). 

C-branched dendritic structures, based on either ether and amide linkages or simply amide connectivity (iii) Tomalia-type PAMAM dendritic structure, differing from the POPAM by the presence of amide bonds, but keeping the amine AB2 as the branching center and (iv) Fr6chet-type dendritic strnctures, based on ether and phenyl groups as AB2 branching center. Description of the different types of covalent dendrimers reported will follow a classification based on the element content, such as only C, C-N, N-O, C-N-0, or with heteroatoms such as P, Si, and so on. Examples of porphyrin-, thiophene-, carbohydrate-, and fullerene-based dendrimers are described separately, since they can be bound to different types of frameworks. 

Hardwood lignins present in their structure both guaiacyl- and syringyl-propane units. Lignin contains mainly glycerol-aryl ether hnkages, but there are also present various types of C-C bonds which may act as cross-linkages between relative short, linear chains of phenyl-propane units. 

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