Substituents, solubility

Because of this wide range of applications, much effort was dedicated to the design and synthesis of new molecules with optimized TPA efficiency in this context, the characteristics of the designed molecules (linear absorption, solubility, substituents...) will depend on the targeted application. The TPA response of moleciUes can be imderstood in the context of its TPA cross-section ajpA. which can be measmed using different techniques, such as nonlinear transmission, two-photon induced fluorescence and the Z-scan method although in a pure TPA process ajpA does not depend on the laser pulse duration, the nonlinear absorption can be more efficient in the nanosecond regime than in the femtosecond one, due to excited state reabsorption phenomena [34]. 

These materials are characterized by common techniques such as H NMR, IR, elemental analysis, DSC, and TGA.54 58 59 60 64 68 Other techniques such as electron spin resonance (ESR),54 magnetic susceptibilities54 and Mossbauer spectroscopy (when they apply),56,58 60 64 71 uV-visible spectroscopy,58,59 60 61 64-67 and solid-state electric conductivity measurements5456 59-63 66 67 71 were also employed. These materials were carefully compared to model bis(mono-isocyanide) adducts for better understanding of the physical properties. Important solubility problems are often observed when no alkyl side chain is used. So, these more soluble substituents are incorporated either on the macrocycles or the bridging ligands for better characterization. 

P-substituted porphyrins in organic solvents or membranes is the shifted face-to-face dimer found in crystal structures (Fig. 6.2.15a). Here one usually finds that an electron-rich pyrrole ring of one porphyrin sits atop the electron-poor center of the other porphyrin. Water-soluble substituents, in particular the most common acetic and propionic acid side chains, lead to amphiphilic bilayers (Fig. 6.2.15c) (Fuhrhop, 1976 Hunter and Sanders, 1990). 

With increasing environmental concerns, the development of water-based ICPs and their complex becomes a necessity. Extensive research has been conducted in this field, especially for polyaniline. Generally, water-based polyaniline can be obtained by three methods introduction of water-soluble substituent to backbone to gain water-soluble polyaniline [158, 159], emulsion polymerization to obtain water-dispersed polyaniline [160-163], and the cormterion-induced processability of doped polyaniline using a hydrophilic protonic acid [164, 165). The first two methods have a common problem of purification and efficiency. In contrast, the pure polyaniline is used in counterion-induced processability of doped polyaniline. The purification and efficiency problems do not exist with this method, so it is the most promising way to obtain water-based polyaniline. 

Introduction of water-soluble substituents, such as anionic, cationic and non-ionic moieties, is a useful way to obtain water-soluble pillar[5]arenes. The first water-soluble pillar[5]arene synthesized by our group was a pil-lar[5]arene with 10 carboxylate moieties H5.11 (Figure 5.14). ... 

Water-soluble pillar[6]arenes can be prepared using the same method as the synthesis of water-soluble pillar[5]arenes. The introduction of water-soluble substituents, such as cationic, anionic and nonionic moieties, allows pillar[6]arenes to solubilize in aqueous media. The first water-soluble pillar[6]arene was synthesized by Huang and co-workers, by introducing 12 carbojylate moieties (Figure 5.31, H5.36). H5.36 could capture paraquat (Table 5.9, run 145, G5.117) in water with a high association constant [ T= (1.02 0.10) x 10 M ], which is much higher than that of the anionic water-soluble pillar[5]arene H5.11 [Table 5.4, run 63, K= (8.20 1.70)xl0 M... 

Several alternative direct methods have been employed to increase the molecular weight and processability of PPP. The key is the incorporation of solublizing substituents, such as long alkyl or alkoxy chains. Mullen reported... 

Two approaches to quantify/fQ, i.e., to establish a quantitative relationship between the structural features of a compoimd and its properties, are described in this section quantitative structure-property relationships (QSPR) and linear free energy relationships (LFER) cf. Section 3.4.2.2). The LFER approach is important for historical reasons because it contributed the first attempt to predict the property of a compound from an analysis of its structure. LFERs can be established only for congeneric series of compounds, i.e., sets of compounds that share the same skeleton and only have variations in the substituents attached to this skeleton. As examples of a QSPR approach, currently available methods for the prediction of the octanol/water partition coefficient, log P, and of aqueous solubility, log S, of organic compoimds are described in Section 10.1.4 and Section 10.15, respectively. 

The solubility of hydrogen chloride in solutions of aromatic hydrocarbons in toluene and in w-heptane at —78-51 °C has been measured, and equilibrium constants for Tr-complex formation evaluated. Substituent effects follow the pattern outlined above (table 6.2). In contrast to (T-complexes, these 7r-complexes are colourless and non-conducting, and do not take part in hydrogen exchange. 

The colors of azo compounds vary with the nature of the aryl group with its substituents and with pH Substituents also affect the water solubility of azo dyes and how well they... 

Most xanthene dyes are classified as basic dyes by their method of appHcation acid dyes can be produced by introduction of sulfonic acid groups. The fluoresceins, which contain carboxy and hydroxy substituents, are also acid dyes for coloration of silk. Some of the fluoresceins in which the carboxy group has been esterified, are soluble in alcohol or other organic solvents and can be classified as solvent dyes. Mordant dyes can be produced by introducing o-dihydroxy or sahcyhc acid groups (2), which when metallised can have very good lightfastness. 

There is a wide variety of dyes unique to the field of hair coloring. Successive N-alkylation of the nitrophenylenediamines has an additive bathochromic effect on the visible absorption to the extent that violet-blue dyes can be formed. Since the simple A/-alkyl derivatives do not have good dyeing properties, patent activity has concentrated on the superior A/-hydroxyalkyl derivatives of nitrophenylenediamines (29,30), some of which have commercial use (31). Other substituents have been used (32). A series of patents also have been issued on substituted water-soluble azo and anthraquinone dyes bearing quaternary ammonium groups (33). 

Pyrrole is soluble in alcohol, benzene, and diethyl ether, but is only sparingly soluble in water and in aqueous alkaUes. It dissolves with decomposition in dilute acids. Pyrroles with substituents in the -position are usually less soluble in polar solvents than the corresponding a-substituted pyrroles. Pyrroles that have no substituent on nitrogen readily lose a proton to form the resonance-stabilized pyrrolyl anion, and alkaU metals react with it in hquid ammonia to form salts. However, pyrrole pK = ca 17.5) is a weaker acid than methanol (11). The acidity of the pyrrole hydrogen is gready increased by electron-withdrawing groups, eg, the pK of 2,5-dinitropyrrole [32602-96-3] is 3.6 (12,13). 

Pyrrohdine [123-75-1] (tetrahydropyrrole) (19) is a water-soluble strong base with the usual properties of a secondary amine. An important synthesis of pyrrohdines is the reaction of reduced furans with excess amine or ammonia over an alumina catalyst in the vapor phase at 400°C. However, if labde substituents are present on the tetrahydrofurans, pyrroles may form (30). 

Attempts have also been made to reduce the odor associated with the peracid in the home laundry. Use of a precursor that generates the peracid of a fatty acid can result in an objectionable odor in the wash bath (106). This odor is exacerbated by the higher piC of the peracid versus its parent acid resulting in a greater proportion of the peracid in the unionized and therefore less water-soluble form. To mitigate this circumstance, functionalization of the fatty tail typically alpha to the carbonyl has been utilized (112). The modifications include alpha-chloro and alpha-methoxy substituents on the parent acid portion of the precursor ester. 

The triaLkoxy(aryloxy)boranes are typically monomeric, soluble in most organic solvents, and dissolve in water with hydrolysis to form boric acid and the corresponding alcohol and phenol. Although the rate of hydrolysis is usually very fast, it is dependent on the bulk of the alkyl or aryl substituent groups bonded to the boron atom. Secondary and tertiary alkyl esters are generally more stable than the primary alkyl esters. The boron atom in these compounds is in a trigonal coplanar state with bond hybridization. A vacantp orbital exists along the threefold axis perpendicular to the BO plane. 

Properties. MethylceUulose [9004-67-5] (MC) and its alkylene oxide derivatives hydroxypropylmethylceUulose [9004-65-3] (HPMC), hydroxyethylmethylceUulose [9032-42-2] (HEMC), and hydroxybutyknethylcellulose [9041-56-9] (HBMC) are nonionic, surface-active, water-soluble polymers. Each type of derivative is available in a range of methyl and hydroxyalkyl substitutions. The extent and uniformity of the methyl substitution and the specific type of hydroxyalkyl substituent affect the solubifity, surface activity, thermal gelation, and other properties of the polymers in solution. 

Developing agents must also be soluble in the aqueous alkaline processing solutions. Typically such solutions are maintained at about pH 10 by the presence of a carbonate buffer. Other buffers used include borate and, less frequendy, phosphate. Developer solubiUty can be enhanced by the presence of hydroxyl or sulfonamide groups, usually in the A/-alkyl substituent. The solubilization also serves to reduce developer allergenicity by reducing partitioning into the lipophilic phase of the skin (46). 

In the course of developing the Polacolor and SX-70 processes many insulated dye developers were synthesized and investigated. An extensive review of this work is available (21). The insulating linkage, chromophore, and developer moiety can each be varied. Substituents on the developer modify development and solubility characteristics substituents on the chromophore modify the spectral characteristics in terms of both color and tight stability. The attachment of two dyes to a single developer by amide linkage has also been described (22). 

Substituted PPVs have been prepared using similar techniques. The earliest reports described methyl substituents (104,105), and more recentiy alkoxy substituents on the aromatic ring have been incorporated into the polymer stmctures (107—109). The advantage of long-chain alkoxy (butoxy or hexyloxy) substituents is that not only is the precursor polyelectrolyte soluble, but after conversion the substituted PPV is also soluble (110—112). 

Other solvents can be divided into several classes. In hydrogen bond-breaking solvents (dipolar aprotics), the simple amino, hydroxy and mercapto heterocycles all dissolve. In the hydrophobic solvents, hydrogen bonding substituents greatly decrease the solubility. Ethanol and other alcohols take up a position intermediate between water and the hydro-phobic solvents (63PMH 1)177). 

From the data reported in (63PMH(l)177) it was concluded that hydrophobic substituents reduce the solubility of pyrazole in water (at 20 °C pyrazole, 1 part in 2.5 3,5-dimethyl-pyrazole, 1 part in 52). Another determination gives the following values for the solubilities of pyrazole at 25 °C in water, benzene and cyclohexane (expressed as g/100 g of solvent) 130, 18 and 3 (66AHC(6)347). Indazole is soluble in hot water and most organic solvents, but less so in cold water. 

Isoxazole dissolves in approximately six volumes of water at ordinary temperature and gives an azeotropic mixture, b.p. 88.5 °C. From surface tension and density measurements of isoxazole and its methyl derivatives, isoxazoles with an unsubstituted 3-position behave differently from their isomers. The solubility curves in water for the same compounds also show characteristic differences in connection with the presence of a substituent in the 3-position (62HC(17)1, p. 178). These results have been interpreted in terms of an enhanced capacity for intermolecular association with 3-unsubstituted isoxazoles as represented by (9). Cryoscopic measurements in benzene support this hypothesis and establish the following order for the associative capacity of isoxazoles isoxazole, 5-Me, 4-Me, 4,5-(Me)2 3-Me> 3,4-(Me)2 3,5-(Me)2 and 3,4,5-(Me)3 isoxazole are practically devoid of associative capacity. 

---