Acid waves

Acidic waving systems based on mercaptans have recently achieved some popularity. The preferred mercaptan is glyceryl thioglycolate [30618-84-9] which is relatively odorless and provides sufficient active anionic mercaptide species at a neutral pH. 

Acid waves are generally based on glycerol monothioglycolate (GMT) although some bisulfite systems are sold as acid waves. For a GMT wave, the waving lotion itself consists of two parts because GMT is not stable for long periods of time in water (Table 3-5). 

To make the acid wave, for Part I of the waving lotion, add glycerol thioglycolate to glycerine (oxygen free) in an inert atmosphere taking the same precautions as described previously for the thiol wave. For Part If of the... 

Table 3-5. Waving lotion for an acid wave based on GMT. ...

A comparison of polarographic results for reduction of maleic and fumaric acids indicates that the fumaric acid waves occur at more negative potentials. The greater thermodynamic stability of fumaric acid (the trans isomer), is consistent with this behavior. 

Fig. 4. Dependence of the height of the maleic acid wave on its concentration.

Nonetheless, one observation is accounted for by a simple empirical extension of the above theory, the undamped propagation of a high-density polymer pulse as illustrated in Figure 9.5. In this experiment, the whole cylinder is initially in the swollen F state. An acid perturbation is made at the bottom end of the cylinder. This induces a transition to the collapse state of the gel, which starts to invade the swollen upper part. Yet, after some time, the collapsed part of the cylinder slowly reswells and relaxes back to the stable swollen state. The phenomenon can be explained by a chemomechanical version of the propagation of an excitability wave [13]. After the initial acid perturbation, the core of the cylindrical OSFR switches to the acid-core reacted state. The acid core contaminates the neighboring unreacted swollen part by diffusion, which, in turn, shrinks, following the acid wave. But the collapse of the gel undershoots the critical size Rinf below which the reacted acid state is stable. Diffusion from the boundary overtakes the reaction, the composition... 

Fig. 9. i-E Curve In 0.1 N sodium hydroxide solution. 1) Beginning of peracetic acid wave 2) beginning of oxygen wave 3) limiting current for peracetic acid. 

The remarkable feature about Eq. 19.4-8 is that it predicts that the dissolution rate within the pores is negative, because all terms in the brackets in Eq. 19.4-8 are positive. In physical terms, this means that Ca(OH)2 will precipitate in front of the acid wave shown in Fig. 19.4-1. This predication is verified experimentally dissolution can produce precipitation. 

When we compare the equilibrium and the diffusion paths, we see that diffusion of H+ into porous Ca(OH)2 will tend to carry us into the two-phase region, and so produce precipitation in front of the acid wave. In contrast, for the reaction... 

The reaction involving chlorite and iodide ions in the presence of malonic acid, the CIMA reaction, is another that supports oscillatory behaviour in a batch system (the chlorite-iodide reaction being a classic clock system the CIMA system also shows reaction-diffusion wave behaviour similar to the BZ reaction, see section A3.14.4). The initial reactants, chlorite and iodide are rapidly consumed, producing CIO2 and I2 which subsequently play the role of reactants . If the system is assembled from these species initially, we have the CDIMA reaction. The chemistry of this oscillator is driven by the following overall processes, with the empirical rate laws as given ... 

Consequently, when D /Dj exceeds the critical value, close to the bifurcation one expects to see the appearance of chemical patterns with characteristic lengtli i= In / k. Beyond the bifurcation point a band of wave numbers is unstable and the nature of the pattern selected (spots, stripes, etc.) depends on the nonlinearity and requires a more detailed analysis. Chemical Turing patterns were observed in the chlorite-iodide-malonic acid (CIMA) system in a gel reactor [M, 59 and 60]. Figure C3.6.12(a) shows an experimental CIMA Turing spot pattern [59]. 

SjOl- -0.15 IM strong acid anodic mercury wave... 

Acetic acid is also transported ia barges, sometimes ia amounts of 1500 to 1750 tons. Acetic acid is not as hygroscopic as some other anhydrous organic substances, but barge shipments occasionahy have specification problems because of wave splashing iato the tanks or other careless handling. 

Waving Lotions. The reagent most frequently used for the reduction of hair is thioglycolic acid [68-11-1]. Although a variety of other mercaptans have been screened (51), none has been able to match the unique combination of efficacy, safety, and low cost that is a hallmark of thioglycolic acid. 

Health and Safety. The dermal toxicology of alkaline solutions of thioglycolic acid has been reviewed extensively (63—65). The reagent has been found harmless to normal skin when used under conditions adopted for cold waving. Some irritation is observed on abraded skin but this appears to be associated with the alkaline component of the waving solution (65). Hand protection is recommended for the professional hairdressers who routinely handle these products. 

Cysteine is used as a reductant for cold wave treatment in place of thioglycoHc acid. A/-Lauroylarginine ethyl ester [48076-74-0] is appHed as the hydrochloride as a preservative. Urocanic acid [104-98-3] hich. is derived from histidine is used in skin cream as a uv absorber (235). 

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