Solubility problems

Numerous attempts to determine the equilibrium constants using titration microcalorimetry failed, due to solubility problems encountered at the higher concentrations of catalyst and dienophile that are required for this technique. 

Analogous studies on dienophiles 5.1c and 5.1g in SDS and Zn(DS)2 lead to essentially the same conclusions. Figure 5.9 shows the relaxation data for 5.1g in Zn(DS)2 solutions. The corresponding data for 5.1c could not be measured due to solubility problems. Analogously, Figure 5.10 shows the relaxation data of 5.1c and 5.1g in SDS solutions. 

The addition proceeds most smoothly with highly functionalized (more polar) steroids as seen in examples by Bernstein and others. The polar reaction conditions pose solubility problems for lipophilic androstane, cholestane and pregnane derivatives. Improved yields can be obtained in some cases by using dimethyl sulfoxide or t-butanol " as solvents and by using sodium A-bromobenzenesulfonamide or l,3-dibromo-5,5-dimethyl hydantoin (available from Arapahoe Chemicals) as a source of positive bromine. The addition of bromo acetate and bromo formate to steroid olefins has been studied to a limited extent. ... 

In aqueous solution especially, the current yield is distinctly lower furthermore, solubility problems can occur when the salt-deficit method is used. In aqueous solution, a-amino- or a-phenyl substituted carboxylates lead mainly to decomposition products, whilst in dry methanol or methanol-pyridine, coupling products were obtained with a-phenyl- and a-acetylaminocarboxylates [49]. 

Several of the compounds had been followed up in a previous project, and solubility problems prevented kttiher development... 

Recently, the scope of the allylic substitution has been extended to sulfinate salts 84 to obtain allylic sulfones 85. Due to solubility problems of both nucleophile 84 and carbonate leaving group, a polar solvent mixture of DMF and 2-methoxyethanol had to be employed, which limits the reaction to the use of a phosphine ligand. Thus, various aryl sulfinates 84 and functionalized carbonates 81 could be converted to the corresponding allylic sulfones 85 with good to excellent yields and regioselectivites and complete retention of stereochemistry (eq. 2 in Scheme 20) [65]. 

Repeating for emphasis - not aU poorly water-soluble compounds are equally solubilized by DMSO. The greaseball compounds will be much better solubilized than the brickdust compounds. The most common range of compound in DMSO stock concentrations in compound storage repositories is 2-20 mM. At conferences, organizations employing 2mM compound in DMSO stock solutions report fewer solubility problems. The downside is that the lower stock concentrations are more Hmited in utility in some absorption, distribution, metabolism, excretion and toxicity assays that require higher compound concentration. 

From our experience with the Bodroux reaction, we knew that the magnesium amide of t-BuNH2 reacts with 33. Recall that, in order to avoid solubility problems in preparation of the magnesium amide reagent, EtMgBr was added to a mixture... 

For pharmaceutical formulations, the simplex method was used by Shek et al. [10] to search for an optimum capsule formula. This report also describes the necessary techniques of reflection, expansion, and contraction for the appropriate geometric figures. The same laboratories applied this method to study a solubility problem involving butoconazole nitrate in a multicomponent system [11],... 

An alternative method to overcome the solubility problem mentioned in the last section is to use bile salts to solubilize lipophilic molecules in the donor wells. Figure 7.51 shows a plot of relative permeability (Pe without bildPe with bile) versus membrane retention, which is related to lipophilicity (Section 7.7.2). As the plot shows, the most lipophilic molecules (carvedilol, propranolol, and verapamil) have attenuated permeabilities (by a factor of 3 in the case of carvedilol). The effective partition coefficient between the PAMPA membrane phase and the aqueous phase containing bile salt micelles [577] is expected to be lower for lipophilic molecules, which should result in lower Pe values. This is evident in the figure. 

Note Solubility problems require mixed micelles for LYC. 

S-Methacryloyloxy-ljl -biadamantane, MBA, (Scheme 4) was efficiently polymerized anionically using [ l,l-bis(4/-trimethylsilylphenyl)-3-methylpen-lyl]lithium as the initiator, prepared in situ by the reaction of s-BuLi with l,l-bis(4-trimethylsilylphenyl)ethylene [17]. The polymerization took place at - 50 °C in order to avoid the solubility problems of the monomer, observed at - 78 °C. Narrow molecular weight distribution block copolymers of rather low molecular weights of PMBA with fBuMA and (2,2-dimethyl-... 

A metal-iodine exchange has been carried out on all three diazine systems under very mild conditions using lithium tri- -butyl magnesate, although only one substrate from each system was used 3-iodo-6-phenylpyridazine, 4-iodo-2-methylthiopyrimidine and 2-iodopyrazine. The pyridazine example was most problematic, possibly due to solubility problems. Aldehydes, benzophenone and diphenyl disulfide were used as the electrophiles <06SL1586>. 

Any solubility problem involving PbCl2 involves the equilibrium ... 

Particularly desirable among film deposition processes are solution-based techniques, because of the relative simplicity and potential economy of these approaches. However, the covalent character of the metal chalcogenides, which provides the benefit of the desired electronic properties (e.g., high electrical mobility), represents an important barrier for solution processing. Several methods have been developed to overcome the solubility problem, including spray deposition, bath-based techniques, and electrochemical routes, each of which will be discussed in later chapters. In this chapter, a very simple dimensional reduction approach will be considered as a means of achieving a convenient solution-based route to film deposition. 

Lor the next condensation, the reaction progress was scanned at both 90°C and 120°C, since it was anticipated that lower reaction temperatures would present insurmountable solubility problems. The construe-... 

Fluorination of low-molecular-weight linear oligomers 7 (n = 7-12) also proceeded cleanly. In this case Krytox was found to be a better solvent because of solubility problems encountered with FC-75. The product 11 was obtained in very good yield, and both H-NMR (which shows no signals) and 19F-NMR are in accord with essentially complete replacement of all the hydrogen atoms by fluorine. That little fragmentation occurred was shown by GPC analysis (M. 3200). 

Finally, in a method originated by Witt [22], which is occasionally useful for the diazotisation of stable amines of high relative molecular mass that pose solubility problems, the amine is dissolved in nitric acid before the addition of sodium metabisulphite. Nitrous acid is produced in the medium according to Scheme 4-9, enabling diazotisation to proceed. 

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