Higher cyclodextrins

Almost no influence of the methylated /i-cyclodextrin on the yield can be observed if no additional organic solvent (except for butadiene or the product) is used as the non-polar phase. With hydroxypropyl-jd-cyclodextrin a decreased yield is obtained and the phase separation is more difficult. If cyclohexane or n-octane is added as the non-polar solvent the conversion and the yield increase with increasing cyclodextrin concentration up to a concentration of about 2 mol % cyclodextrin based on butadiene. Because of the high viscosity of the solution no further improvement can be achieved using higher cyclodextrin concentrations. Lower yields are obtained by use of a-cyclodextrin as compared with the methylated j8-cyclodextrin. 

The cyclodextrins can tolerate relatively high buffer concentrations and are stable from pH 3 to pH 14. However, the stability of the silica matrix restricts the pH range from 3. 0 to about 7.0, as silica is significantly soluble at a pH of 8.0 and higher. Cyclodextrin type stationary phases may be operated in the polar or reversed phase mode. As with the other LC stationary phases, mobile phases with high water contents have little dispersive properties and thus the dispersive interactions with the stationary phase can be exploited. Conversely, if strongly dispersive... 

This result indicates the disappearance of two molecules of ADP and the formation of one molecule each of AMP and ATP they should reach an equilibrium. The dependence of ATP formation on the cyclodextrin concentration is shown in Fig. 4. At the higher cyclodextrin concentration, the induction period increased and the decrease in ATP concentration was depressed. ATP formation depended on the g-cyclodextrin concentration. With 1/5 to 3 times the equimolar amount of g CD to ADP, the ATP formation was not so different but 6 mol excess g-CD caused slow formation of ATP. The addition of cyclohexanol caused a... 

Comparisons of LC and SFC have also been performed on naphthylethylcar-bamoylated-(3-cyclodextrin CSPs. These multimodal CSPs can be used in conjunction with normal phase, reversed phase, and polar organic eluents. Discrete sets of chiral compounds tend to be resolved in each of the three mobile phase modes in LC. As demonstrated by Williams et al., separations obtained in each of the different mobile phase modes in LC could be replicated with a simple CO,-methanol eluent in SFC [54]. Separation of tropicamide enantiomers on a Cyclobond I SN CSP with a modified CO, eluent is illustrated in Fig. 12-4. An aqueous-organic mobile phase was required for enantioresolution of the same compound on the Cyclobond I SN CSP in LC. In this case, SFC offered a means of simplifying method development for the derivatized cyclodextrin CSPs. Higher resolution was also achieved in SFC. 

Monflier et al. (1997) have suggested Pd catalysed hydrocarboxylation of higher alpha olefins in which chemically modified P-cyclodextrin (especially dimethyl P-cyclodextrin) is u.sed in water in preference to a co-solvent like methanol, acetone, acetic acid, acetonitrile, etc. Here, quantitative recycling of the aqueous phase is possible due to easy phase separation without emulsions. A similar strategy has been adopted by Monflier et al. (1998) for biphasic hydrogenations for water-in.soluble aldehydes like undecenal using a water-soluble Ru/triphenylphosphine trisulphonate complex with a. suitably modified p-cyclodextrin. 

It has been claimed that complexes of P-cyclodextrin with anionic surfactants, notably higher fatty alcohol ethoxylates, improve scouring efficiency on cotton and wool in laboratory-scale processing [34]. Residual surfactants carried over from preparation can have undesirable effects in subsequent processing. When cyclodextrins complex with surfactants, their surface activity is reduced. Hence cyclodextrins are potentially useful for the removal of residual amounts of surfactants from substrates [35]. The use of a- and P-cyclodextrins has been studied in this context with one cationic, one anionic and four... 

JOC3338, 2003OL3839>. The addition of ot-cyclodextrin (lequiv) increased the yield, but did not influence the translcis-selectivity <1996J(P1)1113>. The higher yield of 79 in aqueous medium was explained as a result of the hydrophobic effect on a reactant encapsulated in a cavity surrounded by a hydrogen-bonded network of water molecules <2001JOC3338>. 

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