Acetate modification

It should be noted that complete blocking of all amines on proteins with sulfo-NHS acetate may cause precipitation or loss of native structure and function. The acetate modifications... 

FIGURE 13.7 The polymer-analt ous reaction to give the hydrophobized ketal dextran [102]. The acetal modification is achieved by reaction of dextran 36 with 2-ethoxypropene 37 to give the poorly water-soluble dextran ketal This change in dextran solubility enables 38 to be fabricated into particulates using nonaqueous media [103-106]. 

The cysteine acetate modification (fish, egg, meat). containing more than O.lmg of total mercury/kg. 

Excess mercuric ions were added to an aqueous liver suspension containing known amounts of a methylmercury salt. The analysis was performed according to the cysteine acetate modification, ... 

For egg-yolk with low content of methylmercury the cysteine acetate procedure gave less than 90% recovery, (Method B described earlier). with the combined method using cysteine and mercuric ions the recovery of methylmercury salt decreased almost to zero. But for sediments in aquaria and sludge, which similarly could not be analysed by the original cysteine acetate modification, the combined method gave good results (Table 16). The combined cysteine/mercuric ion method was also applied to fish muscles with good recoveries. ... 

Finally on studies on the determination of nitric oxide, platinum electrodes sealed in glass were mocUfied with Nation and cellulose acetate. Modification with Nation was achieved by placing over a freshly polished electrode a lOpl volume of a 0.5% (w/v) solution of Nation in ethanol and allowing the solvent to dry in air. Modification with cellulose acetate was carried out in a similar fashion with an acetone/cyclohexanone solution (2%) of cellulose acetate and again employing a 10 il volume. Prior to use, the electrode was contacted with a phosphate buffer solution for 30 min. to allow the modifying layers to equilibrate and swell. The determination of NO was carried at +0.90V vs SSCE to ensure that the response was mass transport limited. 

I) A slightly better yield of ester can be obtained by increasing the quantity of acetic acid to 90-120 g. and refluxing for 12-18 hours. This modification is not worth while in a student s preparation. 

A more active product is obtained by the following slight modification of the above procedure. Dissolve the succinimide in a slight molar excess of sodium hydroxide solution and add the bromine dissolved in an equal volume of carbon tetrachloride rapidly and with vigorous stirring. A finely crystalline white product is obtained. Filter with suction and dry thoroughly the crude product can be used directly. It may be recrystallised from acetic acid. 

Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

Modifications of Processes Based on Air Oxidation ofp-Xylene. Since the mid-1970s, starting in Japan, several companies have developed oxidation processes to yield relatively pure forms of terephthaUc acid without a separate purification. These products, normally called medium purity terephthahc acids, contain 200—300 ppm 4-formylbenzoic acid and trace amounts of acetic acid and thus do not meet normal specifications for the highest purity grades available (80,81). 

A related but distinct rhodium-catalyzed methyl acetate carbonylation to acetic anhydride (134) was commercialized by Eastman in 1983. Anhydrous conditions necessary to the Eastman acetic anhydride process require important modifications (24) to the process, including introduction of hydrogen to maintain the active [Rhl2(CO)2] catalyst and addition of lithium cation to activate the alkyl methyl group of methyl acetate toward nucleophilic attack by iodide. 

Modifications iaclude the use of P-ketoaldehydes as acetals, eg (9), which leads to loss of the formyl group (21) the product ia this example is 5-ethoxycarbonyl-2-methylpyrrole [3284-51 -3]. 

The Perkin reaction is of importance for the iadustrial production of coumarin and a number of modifications have been studied to improve it, such as addition of a trace of iodine (46) addition of oxides or salts of metals such as iron, nickel, manganese, or cobalt (47) addition of catalytic amounts of pyridine (48) or piperidine (49) replacement of sodium acetate by potassium carbonate (50,51) or by cesium acetate (52) and use of alkaU metal biacetate... 

Modifications of epichlorohydrin elastomers by radical-induced graft polymeri2ation have been reported. Incorporated monomers include styrene and acrylonitrile, styrene, maleic anhydride, vinyl acetate, methyl methacrylate, and vinyHdene chloride (81), acryHc acid (82), and vinyl chloride (81,83,84). When the vinyl chloride-modified epichlorohydrin polymers were used as additives to PVC, impact strength was improved (83,84). 

---