Glycolic acid titration

Superficial chemical peels, including salicylic and glycolic acids, and Jessner s peels target the stratum corneum to the papillary dermis. These agents can be safely used to facilitate the resolution of PIH (Figs. 16.2,16.3,16.4 and 16.5). To assess for variability in response and limit further PIH, when possible, chemical peels should be initiated at the lower concentrations and titrated to higher concentrations if necessary to increase efficacy while minimizing side effects (see Darker Skin Section). 

C18-0020. Glycolic acid (HOCH2 CO2 H), a constituent of sugar cane juice, has a p Zg of 3.9. Sketch the titration curve for the titration of 60.0 mL of 0.010 M glycolic acid with 0.050 M KOH. Indicate the stoichiometric point, the buffer region, and the point of the titration where pH- p. S a. Sketch the curve qualitatively without doing any quantitative calculations. 

C18-0022. Choose an indicator suitable for the titration of glycolic acid. What is the color of the solution at the stoichiometric point ... 

The analysis of the content of surfactant actives of betaine solutions is rather complicated. No direct titration method for the determination of the betaine concentration was available in the past, since all methods known have lead to incorrect results due to the presence of protonable by-products such as glycolic acid or free amidoamine (38). A modified titration method has been developed in recent years which gives more accurate results due to the choice of a special solvent mixture (39). The use of methanol and ethylene glycol monomethyl ether allows the almost selective titration of a betaine in its complex solution. 

Loss on ignition measurements and levels of calcium hydroxide, calcium carbonate, basic carbonates, and organic material (e.g. from grinding aids) are determined by thermogravimetric analysis. This technique shows weight loss at characteristic temperatures that can be related to the amount of various phases present. Free (uncombined) lime (CaO) is determined by extraction with ethylene glycol and titration with O.lmoll hydrochloric acid. 

The pKl reported for glycollic acid is 3.882 at 25°. What is the pH at the start, midpoint, and end when 25.00 ml of 0.0500 M glycollic acid is titrated with 0.2000 M NaOH solution First calculate the effective and/or using the new volume at each point. Then get an approximate H. How large will the activity effect be on the at the conditions, and will equation (3-2) be required to get a result to 0.01 pH unit ... 

The first end-point measures the excess hydrochloric acid. The additional titrant to the second end-point measures the betaine. A third point of inflection, corresponding with the titration of glycolic acid, monochloro-acetic acid and free amine, is found if the titration is continued further. These extraneous substances, being titrated over a different part of the curve, do not interfere, and the authors [19] confirmed by experiment that this was so. 

The other methodology involves the protometric titration of the formic acid that was formed. It necessitates first adding ethylene glycol to the solution once the oxidization reaction has finished. Ethylene glycol destroys the excess of periodic acid, which is transformed into iodate ions. Formic acid titration is achieved by pH-metry, the equivalent point being taken for pH=7. Beyond pH=7, the equilibria between the different periodate ions induce the formation of hydroxide ions, which distort the determination. 

In general, glycolic acid peels are well tolerated in darker skinned people. Side effects are substantially minimized when peel concentrations are gradually titrated from the lower concentrations of 20-35% to the full-strength 70%. Glycolic acid peels are most advantageous when treating darker skin types with sensitive skin. 

Alkyldimethylbetaine and free amine can be determined by potentiometric acid-base titration (12). For titration of the betaine, the sample is dissolved in a mixture of 10 1 methyl isobutyl ketone/isopropanol to which a little HCl has been added. Three breaks are observed on titration with ethanolic KOH, corresponding respectively to excess HCl, the betaine, and combined impurities amine, glycolic acid, and monochloracetic acid (see Fig. 1). Carbon dioxide must be excluded during the titration. Sodium chloride is insoluble in the solvent system and precipitates. The titration is very sensitive to water concentration (16)... 

As an example of the quantitative testing of Eq. (5.47), consider the polymerization of diethylene glycol (BB) with adipic acid (AA) in the presence of 1,2,3-propane tricarboxylic acid (A3). The critical value of the branching coefficient is 0.50 for this system by Eq. (5.46). For an experiment in which r = 0.800 and p = 0.375, p = 0.953 by Eq. (5.47). The critical extent of reaction, determined by titration, in the polymerizing mixture at the point where bubbles fail to rise through it was found experimentally to be 0.9907. Calculating back from Eq. (5.45), the experimental value of p, is consistent with the value =0.578. 

Mesoxalic dialdehyde can be reasonably expected (16,28,50) to undergo normal glycol cleavage and give one mole of formic acid and one mole of glyoxylic acid in fact, when a second molar equivalent of periodate was added to the above solution, two molar equivalents of titratable acid were formed. If an excess of periodate is now added, two molar equivalents of titratable acid remain, but in addition, one molar equivalent of carbon dioxide can be expelled from the solution. Thus, in the overall reaction, one mole of triose reductone is oxidized by three moles of periodate to give two moles of formic acid and one mole of carbon dioxide ... 

The progress of polyester-forming reactions between glycols and dibasic acids is easily followed by titrating the unreacted carboxyl groups in samples removed from the reaction mixture. Simple esterification reactions are known to be acid-catalyzed. In the absence of an added strong acid, a second molecule of the acid undergoing esterification functions as catalyst. The rate of the poly esterification process should therefore be written... 

In the determination of formic acid in more complicated reaction-mixtures (for example, in the presence of buffers,22 69a in solutions containing non-volatile acids,49- 67 and in solutions containing ammonia234), it was necessary to distil the formic acid from the reaction solution (after destruction of the excess periodate with ethylene glycol or arsenite) before it could be titrated. 

Figure 3.22. Fluorescence titrations of anthrylboronic acid 16 (0.75 jiM) at pH 7.4 (20 mAf phosphate buffer) as a function of polyol concentration (+, fructose , t,l,l-tris(hydroxymethyl)ethane a, glucose +, ethylene glycol). All solutions contain 1% (v/v) dimethylsulfoxide (DMSO). (Reproduced from Ref. 26. Copyright 1992 American Chemical Society.)...

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