Amide phases

The top two stationary phases in Figure 12 are the C g and Cg phases, which are the most frequently used phases in reversed-phase LC. Below that, three phases with an embedded polar group are shown the carbamate phases (e.g., SymmetryShield), amide phases (e.g.. Discovery RPAmide C g) and urea phases (such as Prism or Spectrum). It should... 

Enantiomer separation on optically active amino acid, dipeptide, diamide and amide phases by association via hydrogen bonding. " ... 

The chromatography conditions applied are usually the same used for thiamine analysis. A RP chromatography is used for analytical determination, such as ODS stationary phase, C18 or amide phases. The mobile phases are methanol, water or acetonitrile with addition of buffer. 

Smith et al. (128) developed a modified amide phase system to extend the operational stability range of the alkylmalonamide-dodecane system. They obtained a more extensive domain of stability over the temperature and acidity concentration range. 

Owing to the high thermal and long-term stability, amide phases bonded to polysiloxane are regarded as sensitive materials for the sensoric approach to enantiomeric separation. An important factor for the resolution of the stationary material is the number of dimethylpolysiloxane units between the chiral moieties. More than 200 different amide phases have been synthesised and applied for the discrimination of amino acids, lactate esters and many other substances [10]. 

Facklam, C., Pracejus, H., Oehme, G., and Much, H., Resolution of enantiomers of amino acid derivatives by high-performance liquid chromatography in a silica gel bonded chiral amide phase, J. Chromatogr., 257, 118, 1983. 

The mechanism of retention on chiral phases that is based on multiple hydrogen bonding formation involves the formation of base pairs and triple hydrogen bonds between the solutes and the chiral stationary phase 95 Fundamental work in this area has been done by Hara and Dobashi,96 97 using amino acid amide and tartaric acid amide phases. In addition, N,N -2,6-pyridinediyl bis(alkanamides) chemically bonded to silica gel have been described for the resolution of barbiturates 95... 

The amide phase systems are also applicable to preparative scale separations. A semi-preparative bonded column (10 mm i.d. X 25 cm) was prepared, yielding a loading capacity of ca. 1 mg per 1 g packing material. Enantiomeric and diastereomeric pairs of benzyloxycarbonyl and tert-butyloxycarbonyl protected di- and tri-peptides were resolved successfully using this chiral amide-bonded column system. 

Under special conditions (addition of lithium amide, phase-transfer catalysis), compounds with apparently unactivated methylene groups (e.g., 5-methoxy-l-tetra-lone, Lombardo and Mander, 1980) or even with a methyl group at an arylcarbonyl group (Sugihara et al., 1987) undergo diazo transfer with arenesulfonyl azides. This is also the case for esters of 4-arylbut-3-enoic acid and related compounds (Davies et al., 1989, and references therein). 

Both paints and adhesives are commonly formulated as polymer blends or grafts. In fact, some compositions resemble semi-IPN s or AB crosslinked copolymers (Section 8.7). For example, epoxy adhesive resins are often cured with polyamides (Bikerman, 1968). The product is tougher than materials cured with low-molecular-weight amines, possibly because of a separate amide phase in this AB crosslinked copolymer. A more complex molecular architecture is exhibited by the alkyd resins common in oil-based paints (Martens, 1968, Chapters 3 and 4). The major component is a polyester, which often forms a network structure on drying. The polyester component is reacted with various drying oils, such as linseed oil or tung oil (Martens, 1968, Chapters 3 and 4). These oils form an ester link to the polyester structures and also polymerize through their multiple double bonds. Latex paints always contain thickeners, such as cellulosics, poly(acrylic acid), casein. 

The ether-sequences, E, in Fig. 7.61 are only about 3 nm long and the crystallinity in the E-phase is only 1% due to restrictions by the surrounding glassy and 37% crystalline amide-phase. A, of 40 nm molecular chain length. The crystals seem to be located close to the phase boundary. 

Example This example of an HN-C(O) amide torsion uses the AMBER force field. The Fourier component with a periodicity of one (n = 1) also has a phase shift of 0 degrees. This component shows a maximum at a dihedral angle of 0 degrees and minima at both -180 and 180 degrees. The potential uses another Fourier component with a periodicity of two (n = 2). 

Some of the physical properties of fatty acid nitriles are Hsted in Table 14 (see also Carboxylic acids). Eatty acid nitriles are produced as intermediates for a large variety of amines and amides. Estimated U.S. production capacity (1980) was >140, 000 t/yr. Eatty acid nitriles are produced from the corresponding acids by a catalytic reaction with ammonia in the Hquid phase. They have Httie use other than as intermediates but could have some utility as surfactants (qv), mst inhibitors, and plastici2ers (qv). 

Vinyl ethers are prepared in a solution process at 150—200°C with alkaH metal hydroxide catalysts (32—34), although a vapor-phase process has been reported (35). A wide variety of vinyl ethers are produced commercially. Vinyl acetate has been manufactured from acetic acid and acetylene in a vapor-phase process using zinc acetate catalyst (36,37), but ethylene is the currently preferred raw material. Vinyl derivatives of amines, amides, and mercaptans can be made similarly. A/-Vinyl-2-pyrroHdinone is a commercially important monomer prepared by vinylation of 2-pyrroHdinone using a base catalyst. 

Aluminum chloride [7446-70-0] is a useful catalyst in the reaction of aromatic amines with ethyleneknine (76). SoHd catalysts promote the reaction of ethyleneknine with ammonia in the gas phase to give ethylenediamine (77). Not only ammonia and amines, but also hydrazine [302-01-2] (78), hydrazoic acid [7782-79-8] (79—82), alkyl azidoformates (83), and acid amides, eg, sulfonamides (84) or 2,4-dioxopyrimidines (85), have been used as ring-opening reagents for ethyleneknine with nitrogen being the nucleophilic center (1). The 2-oxopiperazine skeleton has been synthesized from a-amino acid esters and ethyleneknine (86—89). 

A AlI lation. 1-Substitution is favored when the indole ring is deprotonated and the reaction medium promotes the nucleophilicity of the resulting indole anion. Conditions which typically result in A/-alkylation are generation of the sodium salt by sodium amide in Hquid ammonia, use of sodium hydride or a similar strong base in /V, /V- dim ethyl form am i de or dimethyl sulfoxide, or the use of phase-transfer conditions. 

Subsequent chlorination of the amide takes place ia a two-phase reaction mixture (a dispersion of diamide ia hydrochloric acid) through which a chlorine stream is passed. The temperature of this step must be maintained below 10°C to retard the formation of the product resulting from the Hofmann degradation of amides. Reaction of the A/,A/-dichloroamide with diethylamine [109-89-7] ia the presence of base yields /n j -l,4-cyclohexane-bis-l,3-diethylurea (35), which is transformed to the urea hydrochloride and pyroly2ed to yield the diisocyanate (36). 

Emulsifiers are incorporated in oil and synthetic mud formulations to maintain a stable emulsion of the internal brine phase. These materials include calcium and magnesium soaps of fatty acids and polyamines and amides and their mixtures (123,127). The specific chemistry of these additives depends on the nature of the continuous phase of the mud, ie, whether diesel oil, mineral oil, or a synthetic Hquid. Lime is added along with the fatty acid to form the... 

Nitrile Process. Fatty nitriles are readily prepared via batch, Hquid-phase, or continuous gas-phase processes from fatty acids and ammonia. Nitrile formation is carried out at an elevated temperature (usually >250° C) with catalyst. An ammonia soap which initially forms, readily dehydrates at temperatures above 150°C to form an amide. In the presence of catalyst, zinc (ZnO) for batch and bauxite for continuous processes, and temperatures >250° C, dehydration of the amide occurs to produce nitrile. Removal of water drives the reaction to completion. 

Instmmental methods of analysis provide information about the specific composition and purity of the amines. QuaUtative information about the identity of the product (functional groups present) and quantitative analysis (amount of various components such as nitrile, amide, acid, and deterruination of unsaturation) can be obtained by infrared analysis. Gas chromatography (gc), with a Hquid phase of either Apiezon grease or Carbowax, and high performance Hquid chromatography (hplc), using siHca columns and solvent systems such as isooctane, methyl tert-huty ether, tetrahydrofuran, and methanol, are used for quantitative analysis of fatty amine mixtures. Nuclear magnetic resonance spectroscopy (nmr), both proton ( H) and carbon-13 ( C), which can be used for quaHtative and quantitative analysis, is an important method used to analyze fatty amines (8,81). 

For more specific analysis, chromatographic methods have been developed. Using reverse-phase columns and uv detection, hplc methods have been appHed to the analysis of nicotinic acid and nicotinamide in biological fluids such as blood and urine and in foods such as coffee and meat. Derivatization techniques have also been employed to improve sensitivity (55). For example, the reaction of nicotinic amide with DCCI (AT-dicyclohexyl-0-methoxycoumarin-4-yl)methyl isourea to yield the fluorescent coumarin ester has been reported (56). After separation on a reversed-phase column, detection limits of 10 pmol for nicotinic acid have been reported (57). 

Zinc chloride melts at 275°C, bods at 720°C, and is stable in the vapor phase up to 900°C. It is very hygroscopic, extremely water-soluble, and soluble in organic Hquids such as alcohols, esters, ketones, ethers, amides, and nitrides. Hydrates with 1, 1.5, 2.5, 3, and 4 molecules of water have been identified and great care must be exercised to avoid hydration of the anhydrous form. Aqueous solutions of zinc chloride are acidic (pH = 1.0 for 6 M) and, when partially neutralized, can form slightly soluble basic chlorides, eg, ZnCl2 4Zn(OH)2 [11073-22-6] and Zn(OH)Cl [14031-59-5]. Many other basic chlorides have been reported (58). 

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