Solubilizing agents esters

Sorbitan esters of fatty acids Emulsifying agent, solubilizing agent, surfactant, stabilizer, suspending agent, vehicle iv... 

In cases where clearness is desired, solubilizing agents are used to improve and stabilize the clarity of a shampoo. Typical clarifying agents include ethanol, isopropanol, propylene glycol, butylene glycol, and sorbitol. Phosphates and short-chain polyethoxylated alcohols and esters have also been used [63],... 

From a regio- and chemoselectivity point of view, the behavior of this class of alkenes is very similar to that observed with unfunctionalized alkenes in biphasic medium. As expected for a biphasic medium, the catalytic activities are comparable with or lower than those observed under similar homogeneous conditions, and strongly dependent on the water-solubility of the alkene. Addition of solubilizing agents is often necessary for high-molecular-mass alkenes. For instance, low-mo-lecular-mass co-alkenecarboxylic acid methyl esters such as methyl 4-pentenoate can be hydroformylated efficiently in biphasic systems whereas methyl esters of higher w-alkenecarboxylic acids such as methyl 13-tetradecenoate require the presence of surfactants (Eq. 1) [9]. 

The solubility of a compound is a barrier that limits its concentration in a solution and therefore the amovmt of material available for absorption. A compovmd s crystal type (polymorph), its particle size, wettability, and the use of solubilizing agents in formulations can all influence solubility. Also, the formation of salts, esters, and complexes with a compovmd can improve its solubility. Solubility is a key parameter for determining the dissolution rate of compovmds, a more informative measure that takes into accovmt the form and particle size distribution in a particular medium. 

That licorice may act as a solubilizing agent in traditional Chinese medicines has been reported by Sasaki et al. (207). Aqueous solutions of the glucoside ester (58) solubilize water insoluble substances such as a-tocopherol and oleanolic acid. This may be a restatement of a description of licorice in the Shen Nong Ben Cao Jing, which states that licorice harmonizes a medicine with any drugs. 

Crown ethers are useful for esterification. Reaction of p-bromophenacyl bromide with potassium salt of a carboxylic acid using 18-crown-6 as the solubilizing agent have been used to prepare p-bromophenacyl esters (Scheme 28). 

Solubilized spices are blended essential oils and/or oleoresins mixed with one of the polysorbate esters (e.g., Polysorbate 80) or other dispersing or solubilizing agents in such a concentration as to give a clear solution when mixed with water. 

Typical commercial ethoxylated sorbitan fatty acid esters are yellow Hquids, except tristearates and the 4- and 5-mol ethylene oxide adducts which are light tan soHds. These adducts, as well as the 20-mol adducts of the triesters, are insoluble but dispersible in water. The monoester 20-mol adducts are water soluble. Ethoxylated sorbitan esters are widely used as emulsifiers, antistatic agents, softeners, fiber lubricants, and solubilizers. In combination with the unethoxylated sorbitan esters or with mono- or diglycetides, these are often used as co-emulsrfiers. The ethoxylated sorbitan esters are produced by beating sorbitan esters with ethylene oxide at 130—170°C in the presence of alkaline catalysts. 

Natural Ethoxylated Fats, Oils, and Waxes. Castor oil (qv) is a triglyceride high in ticinoleic esters. Ethoxylation in the presence of an alkaline catalyst to a polyoxyethylene content of 60—70 wt % yields water-soluble surfactants (Table 20). Because alkaline catalysts also effect transestenfication, ethoxylated castor oil surfactants are complex mixtures with components resulting from transesterrfication and subsequent ethoxylation at the available hydroxyl groups. The ethoxylates are pale amber Hquids of specific gravity just above 1.0 at room temperature. They are hydrophilic emulsifiers, dispersants, lubricants, and solubilizers used as textile additives and finishing agents, as well as in paper (qv) and leather (qv) manufacture. 

Hydroxamic acids constitute an important class of siderophores, which play a major role in iron solubilization and transport. Some of them are important as therapeutic agents. The Michael addition of nitroacetyl proline esters to allyl acrylate followed by Pd(0)-catalyzed intramolecular allyl transfer and subsequent reduction of the nitro group yields a novel class of cyclic hydroxamic acids related to pyroglutamic acid (Scheme 5.9).85... 

It is possible to oxidize alcohols in the presence of free carboxylic acids.206 Nevertheless, sometimes better results are obtained if the acid is protected, for example by methylation.207 Sometimes, free carboxylic acids have a low solubility in cold CH2C12. In such cases, an in situ protection with the silylating agent, bis(trimethylsilyl)acetamide (BSA) normally allows the solubilization of the acid as trimethylsilyl ester, and an easy Swern oxidation. The resulting silylated acid is easily deprotected during the work-up.208... 

The two principal methods for processing hemicellulose to increase the accessibility of cellulose to penetrating agents are to put the hemicellulose into a liquid phase and/or reduce its molecular weight (Figure 6). Such aqueous solvents as alkali solutions solubilize hemicellulose by sodium salt formation and by breaking ester cross-links. Either true solutions or colloidal dispersion may be the mechanism by which the attack the lignin that blocks accessibility to cellulose. 

Another method is the use of esters as alkylating agents in triflic acid172 [Eq. (4.44)]. This method has been used to synthesize. S -methylated phenylene sulfide oligomers (methyl triflate, triflic acid, 25°C, 10 h) and to solubilize poly(phenylenesulfide) by transforming it to poly(arylenesulfonium) salts 62 (methyl triflate, methyl or ethyl formate, triflic acid, 110°C, lOh). In a similar way, alkylation of thianthrene to yield the corresponding sulfonium salts (63) has been achieved using alkyl formates.173... 

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