Quatemisation

The quinoxaline 100, with self-contained donor-acceptor properties, has potential in optoelectronic <06JACS10992>. Electroactive dendrimeric bis-quatemary salts have been prepared by direct quatemisation of pyrazine using dendrimeric benzyl bromides <06TL4711>. 

The thiazole ring system is found in many types of dye. Thiazole-containing sulphur dyes and primuline were considered in section 6.4-2. Quaternised dehydrothio-p-toluidine 6.133 is available as Cl Basic Yellow 1 (6.152). Other derivatives of this intermediate are used as direct dyes, such as Cl Direct Yellow 8 (4-58). The benzothiazole ring appears in various azo disperse dyes [14], quatemisation of which gives useful cationic dyes, an important example being Cl Basic Blue 41 (4.99). Another example containing a quaternised thiazole ring is Cl Basic Red 29 (4-102). 

Further Functionalisation. Molecular features required for the application of the dyes in a particular application are often added after the formation of the dye. The best examples are the groups required for the reactive dyeing of cel-lulosics and other fibres and the quatemisation of dyes used on polyacrylonitrile (see section 2.3.2.1). 

The delocalised charged dyes are dominated by cyanine dyes, exemplified by the azacarbocyanine Cl Basic Yellow 11 (2.27), the diazacarbocyanine Cl Basic Yellow 28 (2.30) and the diazahemicyanine Cl Basic Blue 41 (2.49). Where necessary quatemisation is carried out as a post colour forming reaction. Other structural types include oxazines, thiazines and triphenyhnethane dyes. 

Butler and co-workers studied the quatemisation of 3,5-diaryl-l,2,4-thiadiazoles 77 with trimethylsilylmethyl triflate at 40 °C and observed reaction at N-2 to give salt 78. Desilyation of 78 with caesium fluoride resulted in ring expansion to 2ff-l,3,5-thiadiazines 79 which on heating in ethanolic sodium ethoxide gave 2,4-... 

Green, A.L. 1957. The reaction of quatemised pyridine aldoximes with nerve gases. PTP 606. 

Massing described a synthesis of systematically modified cationic lipids by solid-phase chemistry starting with the immobihsation of (/f)-2,3-epoxy-1 -propanol on 4-methoxytrityl chloride resin [157], Reaction of the epoxide with distinct long-chained amines was followed by reductive animation and tertiary amine quatemisation (see Fig. lib). This interesting method allowed the solid-phase coupling of three different lipophUic moieties on an amino group and the synthesis... 

Information about transmission of chirality in dendrimer molecules also came from various generations of dendrimers derived from optically active alkaloids. Starting from atropine or quinine, corresponding ammonium salts 1 or 2, respectively, of up to the third generation were synthesised by quatemisation at the aliphatic nitrogen with Frechet-type dendritic benzyl bromides (Fig. 4.67) [22]. 

Solladie-Cavallo, A. Solladie, G. Etude de la stereoselectivite de la quatemisation de pyrro-lidines-1,2 disubstituees. Tetrahedron Lett. 

Watling KJ, Aspley S, Swain CJ, Saunders J. [3H]Quatemised ICS 205-930 labels 5-HT3 receptor binding sites in rat brain. Eur J Pharmacol 1988 149 397-398. 

The solid supports used in this study were macroporous co-polymers of vinylpyridine and styrene crosslinked with divinylbenzene. Polymers of this type in the form of beads are available commercially (e.g. Reillex 425) and were also prepared for this study by Purolite. For spectroscopic studies, a more convenient sample morphology was required and thin-film polymers of similar stoichiometry were synthesised by the group of Sherrington at the University of Strathclyde. Full details of the methods used to prepare thin film polymers are reported elsewhere.11 To generate the ion exchange resin, the pyridyl functionalities of the polymer were quatemised with methyl iodide (Eq 1). 

Rhodium complex was loaded onto the quatemised polymer support by the reaction with [Rh(CO)2I]2 in hexane (Eq 2). The resulting polymer beads or films showed the characteristic yellow colour of [Rh(CO)2I2] . An infrared spectrum of the powdered beads (KBr disk) showed two weak v(CO) absorptions of similar intensity at 2056 and 1984 cm 1, consistent with the presence of the cis-dicarbonyl complex, [Rh(CO)2I2]" (2059, 1988 cm 1 in CH2C12). Spectra of a much higher quality and intensity were obtained from polymer films loaded with rhodium complex. These observations of polymer supported [Rh(CO),I,r match those reported in the original study of Drago et al. 

Poly(4-vinylpyridine-co-styrene-co- divinylbenzene) were supplied in the form of beads (Reillex 425 and Purolite ) or prepared as thin films (dimensions ca. 76 x 14 mm x 40-120 pm) at the University of Strathclyde.11 Quatemisation of the pyridine groups was carried out by slow addition of the polymer (typically 1 g) to ethanol (40 cm3) To this was added methyl iodide (2 cm3) and the mixture was heated to 50 °C for 2 hours and then cooled. The quatemised polymer was washed with ethanol followed by acetone and then vacuum dried. 

Polymer was loaded with rhodium complex as follows The quatemised polymer (1 g) was added to a solution of [Rh(CO)2I]2 (15 mg, 26 pmol) in hexane (20 ml) and stirred for 4 hours (until the solution in contact with the polymer beads or films became colourless). The polymer beads/films were filtered and washed with hexane, dried in vacuo and stored under an atmosphere of CO at -10 °C. Iridium complex was loaded in a similar manner using Ph4As[Ir(CO)2I2] (23 mg, 26 pmol) in CH2C12 (20 cm3). 

Catalyst retention can be further optimised if a charged derivative of the (QN)2PHAL-ligand is used. Quatemisation of one of the nitrogen atoms with benzyl bromide affords the cationic ligand (QN)(QN-Benz)PHAL, and indeed recyclability was improved in the presence of this ligand, however at the cost of lower ee, as shown in Scheme 5.14.[66] The addition of one equivalent of tetraethylammonium acetate was found to improve the selectivity. 16 11... 

Alkylation of amines and amides with benzylic halides is an early and useful method for the protection of amines and amides. Primary amines can alkylate twice to give the W,N-dibenzyl derivative, but severe steric congestion prevents quatemisation [Scheme 8.199].410... 

In an attempt to achieve solvent free preparation of ionic liquids, others have reported an improved approach whereby the reaction temperature was moderated by placement of the reaction vessel in a water bath. For example, Chan et al. [108] attempted to moderate the heat of the quatemisation reaction and thereby large scale preparation of imidazolium and pyridinium-based ionic liquids. Water moderation was successfully applied to avoid runaway reactions in the large-scale preparation of a number of ionic liquid precursors under solventless conditions using microwave irradiation ... 

Exposure to oxygen should be minimized and therefore it is often recommended [119] that starting materials are degassed and quatemisation is performed in a sealed vessel or under an inert atmosphere. 

The presence of trace acetone has been shown [119] to lead to more highly coloured quatemisation products and should therefore be completely excluded. 

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