Propylene glycol group

Humectants. In certain foods, it is necessary to control the amount of water that enters or exits the product. It is for this purpose that humectants are employed. Polyhydric alcohols (polyols), which include propylene glycol [57-55-6], C2Hg02, glycerol [56-81-5], C HgO, sorbitol [50-70-4], and mannitol [69-65-8], contain numerous hydroxyl groups (see Alcohols,polyhydric). Their stmcture makes them hydrophilic and... 

Natural Products. Many natural products, eg, sugars, starches, and cellulose, contain hydroxyl groups that react with propylene oxide. Base-cataly2ed reactions yield propylene glycol monoethers and poly(propylene glycol) ethers (61—64). Reaction with fatty acids results ia a mixture of mono- and diesters (65). Cellulose fibers, eg, cotton (qv), have been treated with propylene oxide (66—68). 

Both polyethers and polyesters may be used as polyols. For example, Du Pont use polytetrahydrofuran for Lycra whilst US Rubber originally used a polyester of molecular mass of about 2000 obtained by condensing adipic acid with a mixture of ethylene and propylene glycols. A polyether-based mixture was used for Vyrene 2 introduced in 1967. All the polyols have terminal hydroxyl groups. 

The so-called G-H solvents were introduced by Palit et al.90 they usually consist of 1 1 mixtures of ethylene or propylene glycol and isopropyl or ra-butyl alcohol (with use of the same mixtures in the titrants) the glycol acts as a solvent for polar groups and the alcohol for the non-polar hydrocarbon groups, which explains the solvating power of their mixtures for both salts and soaps, whereas the alcohol chosen is beneficial for wider pH ranges (see Figs. 4.1 and 2). 

Molecular model studies confirm the possibility of the PPG chain to penetrate the [S-CD cavity, but not the a-CD cavity owing to the steric hindrance of the methyl groups on the chain. They also indicate that the [S-CD cavity can accommodate two propylene glycol units. 

The bis(jS-diketonato) Ti(IV) complex [Ti(bzac)2(OEt)2] 35 (budoti-tane, shown as the predominant cis,cis,cis isomer) entered phase I clinical trials in Germany in 1986 for the treatment of colon cancer (186). The complex is very susceptible to aquation, and to minimize this, the coprecipitate (Cremophor EL, 1,2-propylene glycol in ethanol and 35) is dissolved in water prior to administration. As for titano-cene dichloride, liver damage is the dose-limiting side-effect (187). The activity of this class of complexes shows little dependence on the nature of the leaving group (e.g., OEt, Cl), but aromatic substituents... 

From a study of the fluoroacetates so far mentioned, it appears that any compound which can give rise to fluoroacetic acid (or the fluoroacetate ion), either by hydrolysis or by oxidation (or both), is toxic. The toxic grouping is thus F-CH2-CO, and any substitution in this radical destroys the toxicity as far as relatively simple compounds are concerned. We had reached this conclusion by May 1943.1 We subsequently showed that esters of / -fluoropropionic acid were non-toxic, whereas esters of y-fluorobutyric acid were shown by American workers to be toxic. In 19442 we reported the synthesis of ethyl 5-fluoro-pentanecarboxylate, F,[CH2]g C02Et (I). This is a stable, colourless liquid and we showed that it possessed very potent toxic properties of the fluoroacetate type. By subcutaneous injection of the propylene glycol solution into mice the l.d. 50 was 4 mg./kg. Methyl fluoroacetate (II) may be taken as a convenient standard (p. 115) and has a l.d. 50 of about 6 mg./kg. for saline solutions, and 15 mg./kg. for propylene glycol solution.3 Therefore ethyl 5-fluoropentanecarboxylate was about 7 times as toxic as methyl fluoroacetate (molecule for molecule).4... 

Propylene glycol. looks like propane with hydroxyl groups, -OH, substituted for a hydrogen on two adjacent carbons. Propylene glycol is also used to make polymers and in a variety of smaller applications such as solvents, humectants, and food additives. 

Hydroxy-terminated polyester (HTPS) is made from diethylene glycol and adipic acid, and hydroxy-terminated polyether (HTPE) is made from propylene glycol. Hydroxy-terminated polyacetylene (HTPA) is synthesized from butynediol and paraformaldehyde and is characterized by acetylenic triple bonds. The terminal OH groups of these polymers are cured with isophorone diisocyanate. Table 4.3 shows the chemical properties of typical polymers and prepolymers used in composite propellants and explosives.E4 All of these polymers are inert, but, with the exception of HTPB, contain relatively high oxygen contents in their molecular structures. 

Moreover, flexible foams are characterized by utilization of special emulsifiers in their synthesis yielding an open-cell architecture, whereas for rigid foams emulsifiers are chosen that create more closed-cell structures. As diisocyanate for both types, the commercially available mixture of 80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate is especially suitable. If foam formation is to take place at room temperature, and especially when hydroxy compounds with secondary hydroxy groups are used [poly(propylene glycol)s], the presence of a catalyst is generally required (see Sect. 4.2.1). 

The facile addition of primary and secondary amines to Cjq has been used to synthesize polymer-bound Cjq [126-133]. Solutions of precursor polymers containing primary amino groups in the side chain or secondary amino groups in the main chain [132] were allowed to react with CgQ in a "buckybalT fishing process. Fullerene end capped polymers (type V) are accessible by reaction of amino-terminated polystyrene [128], poly(ethylene glycol) or poly(propylene glycol) [129] with Cgo. 

---