Glycollate, structure

A far more sensitive criterion for the presence of head-to-head arrangements in poly-(vinyl alcohol) is the decrease in molecular weight caused by addition of periodic acid or periodate ion to an aqueous solution of the polymer.Wherever a 1,2-glycol structure occurs, the chain is split as follows ... 

The failure of a compound to undergo periodate oxidation can not be regarded as positive proof that it contains no 1,2-glycol structures. If the glycol is securely locked in a trans position, oxidation has been shown not to occur. This resistance has been encountered in the bicyclic anhydro hexoses, for example, l,6-anhydro-/3-D-glucofuranoseM and 1,6-anhydro-a-D-galactofuranose.54 This work has already been summarized in this... 

A comparison of coatings formulations based on various glycols to determine the effects of the various glycol structures on the performance properties of the coatings has been made. Properties compared included degree of cure, flexibility, hardness, hydrolytic stability, processibility, chemical and stain resistance, and viscosity (18,19). 

Propagation of the polymerization occurs nearly exclusively by head-to-tail reactions, with only a small fraction of head-to-head reactions. The relative ratio of these two reactions is only a function of temperature and has been found to be independent of molecular weight, polymerization solvent, and method of polymerization. The head-to-head addition yields a 1,2-glycol structure in the resulting poly(vinyl alcohol), which in turn influences the degree of crystallinity, strength, solubility, and thermal stability. 

In this experiment, the method of Flory and Leutner will be used to determine the fraction of head-to-head attachments in a single sample of PVOH. The method depends on the fact that in PVOH a head-to-head linkage is a 1,2-glycol structure, and 1,2-glycols can be specifically and quantitatively cleaved by periodic acid or periodate ion. Treatment of PVOH with periodate should therefore break the chain into a number of fragments, bringing about a corresponding decrease in the effective molar mass. All that is required is a measurement of the molar mass of a specimen of PVOH before and after treattnent with periodate. 

Determination of Frequency of Head-to-Head Occurrences. We wish to calculate the fraction of linkages that are head to head (that is, the ratio of backward monomer units to total monomer units), on the assumption that degradation arises exclusively from cleavage of 1,2-glycol structures and that all such stractures are cleaved. Let us denote this ratio by A. It is equal to the increase in the number of molecules present in the system, divided by the total number of monomer units represented by all molecules in the system. Since these numbers are in inverse proportion to the respective molar masses,... 

Periodate lignin may be another type of lignin preparation representative of whole lignin in wood [46]. Wood meal suspending in water with a small amount of acetic acid is treated with sodium metaperiodate at room temperature, by which vic-glycol structures in carbohydrates are cleaved to give aldehydes. After the subsequent reduction of aldehydes to alcohols, carbohydrates are readily hydrolyzed even at room temperature in a mild acid condi-... 

No 3-hexanone was observed. This lack of 3-hexanone and the absence of any unsaturated alcohol products in the pyrolyzate are further arguments for vinylation at the olefinic rather than the allylic position and for the 1,2- rather than 1,3-glycol structure for the diol monoacetates. It is still possible that a 1,3-diol diacetate was formed specifically, without the formation of a 1,3-diol monoacetate, but this is at best unlikely. Reduction of the hexenyl acetate portion of the pyrolyzate showed the product to be 100% primary acetate. 

The yellow color with ferric chloride was suggestive of hydroxyl a to carboxyl, confirmed by lead tetraacetate oxidation which furnished 1 mole equivalent of carbon dioxide (140, 220). A negative reaction with periodate established the absence of a glycol structure, and the acid absorbed no hydrogen in the presence of either platinum oxide or Raney nickel. The IR-spectrum indicated the absence of C = 0 and C = C, but confirmed the presence of the carboxyl and hydroxyl, groups. Bradbury (220) accepts the presence of bands at 878, 1153, 1213, and 1266 cm., which do not all appear in the spectra of other necic... 

Shogren R.L., Swanson C.L., Thompson A.R., Extrudates of cornstarch with urea and glycols Structure/mechanical property relations, Starch/Starke, 44, 1992, 335-338. 

Jiang, H. Manolache, S. Wong, A. C. Denes, F. S., Synthesis of Dendrimer-Type Poly(ethylene glycol) Structures from Plasma-Functionalized Silicone Rubber Surfaces. J.Appl. Polym. Sci. 2006,102, 2324-2337. 

The occurrence of a species-specific bile acid in pig bile [Haslewood (1) Haslewood and Sjovall (2)] and of two such acids in rat bile [Bergstrom and Sjovall (3) Hsia et al. (4) Matschiner et al. (5)] was observed almost simultaneously. After their isolation and characterization, these acids were found to be isomeric 3a,6,7-trihydroxy-5/5-cholanic acids. The acid from pig bile was named hyocholic acid [Haslewood (6) Ziegler (7)], and the two acids from rat bile were named a- and /3-muricholic acids [Hsia et al. (8)]. The fourth isomer of these glycols was identified as a metabolite of hyodeoxycholic acid (3rt,6a-dihydroxy-5 9-cholanic acid) in the rat [Matschiner et al. (9, 10)], and was named ry-muricholic acid [Hsia et al. (8)]. The vicinal glycol structures in ring B of these acids are unique features, but even more unique are their species-specific characteristics which are particularly demonstrated in the metabolic pathways that lead to their formation. 

The structure of hyocholic acid was proposed by Haslewood (24) and by Ziegler (7) to be 3a,6a,7 -trihydroxy-5 -cholanic acid (I, Fig. 1). Since it was known that pig bile contains hyodeoxycholic acid (3a,6a-dihydroxy) and chenodeoxycholic acid (3a,7a-dihydroxy) the bile was assumed to contain possibly also an acid with both 6a- and 7a-hydroxyl groups. Chemical evidence for the vicinal glycol structure in hyocholic acid was found after chromic oxidation. The product, 3-keto-6,7-secocholanic acid-6,7-dioic... 

Hyocholic acid forms an acetonide (IV). Although it could not be crystallized [Ziegler (7) Haslewood (24)], its formation was substantiated by chromatographic mobility and data of quantitative acetylation. Formation of the acetonide gave evidence for the m-glycol structure in hyocholic acid. The a-orientation of this 6,7-glycol was deduced from data of molecular rotations. Based on values from Barton and Klyne (34), the calculated molecular rotation of 3a,6a,7a-trihydroxy-5/3-cholanic acid would be —13 and that of the 3a,6a,7 -isomer, +249. The observed molecular rotation of hyocholic acid was +19. It was therefore concluded that hyocholic acid is the 3a,6a,7a rather than the 3a,6/3,7/3-isomer [Ziegler (7)]. 

This synthetic strategy is based on the formation of direct micelles of Pluronic FI 27 in water. Pluronic FI 27 is a non-ionic triblock copolymer surfactant terminating in primary hydroxyl groups, and presenting a poly(ethylene glycol)-poly (propylene oxide)-poly(ethylene glycol) structure (PEG-PPO-PEG, MW 12600), that is relatively non-toxic. 

Polyesters contain carboxylic ester linkages (-0-C0-) in the backbone. Polyesters are synthesized by reaction of a diol and a dicarbonic acid, e.g. poly(ethylene terephthalate) (PET) by polycondenastion of ethylene glycol and dimethyl terephthalate. Poly(butylene terephthalate) (PBT) is produced by reaction with butylene glycol. Structures of PET and PBT are shown in Fig. 2.2.7. 

We have reported recently synthesis of a polyesterimide (PEI) firm trimellltic acid anhydride, 4,4 -diaminodi ienyl methane and ethylaie glycol.structural of the repeat unit of PEI may be shCMn as follows ... 

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