Neat reactant

The fate of the ion pair iatermediate depends on the stmcture of the amine and the reaction conditions. Certain tertiary amines, eg, dimethylaruline (DMA), react with specific diacyl peroxides such as diben2oyl peroxide (BPO) to generate free radicals at ca 20°C. Some reactions, eg, DMA—BPO, are explosive when neat reactants are mixed. Primary and secondary amines do not yield free radicals. 

Quinoxaline and phenacyl bromide gave 1-phenacylquinoxalinium bromide (211) (neat reactants, 60°C, -5 min 30%). ... 

The same substrate (215) with 2-pyridinamine gave pyrido[l, 2 l,2]imi-dazo[4,5-/7]quinoxaline (218) (neat reactants, 220°C, 30 min 80% EtsN, pyridine, reflux, 4 h %) also analogs somewhat similarly. " ... 

Benzylamino)methyl-l,2,3,4-tetrahydroquinoxaline (189) and diethyl oxalate gave 2-benzyM,4a,5,6-tetrahydro-l//-pyrido[l,2-fl]quinoxaline-l,2(3//)-dione (190) (neat reactants, 95°C, 20 h 46%). ... 

Ethyl 7-amino-2,3-dimethyl-6-quinoxalinecarboxylate (196) and urea gave 7,8-dimethylpyrazino[2,3-g]quinazoIine-2,4(l//, 3/7)-dione (197) (neat reactants, 198°C, 20 min 92%) analogs Ukewise. " ... 

Hydrazino-3-methylquinoxaline (247) and phenacyl cyanide gave 2-(3-amino-5-phenylpyrazol-l-yl)-3-methylquinoxaline (248) (EtOH, reflux, 4 h 60% or neat reactants, fused, 5 min >50%) analogs likewise. " ... 

Note The introduction of a passenger cyano group has been exemplified in earlier chapters. A single typical example is given here. 3-Chloro-2-quinoxalinecarbaldehyde (147) and ethyl cyanoacetate gave 2-chloro-3-(2-cyano-2-ethoxycarbonylvinyl)quinoxaline (148) (neat reactants,... 

A typical reason for longer reaction times in the plant is slower overall heat removal rates. And a typical case is batch hydrogenation, with a neat reactant or in solvent. Here all reactants are charged before the batch reaction is initiated. Typical set of reactions is ... 

The feedstreams can consist of either neat reactants or their solutions. When the feedstreams consist of solutions, the reaction mixture is pumped into a polymerization vessel where the reaction that started in the mixing head proceeds to its conclusion. The polymer is subsequently precipitated from solution, separated, dried, and pelletized. Solvent-free mixtures of reactants are pumped directly to a mold where polymerization proceeds. In this case, other additives, such as, fillers or fire retardants, are co-mixed with the reactants in the mixing head. These additives are permanently incorporated into the finished molding. 

Among numerous other studies, Ferrier rearrangement is notable since it proceeds well (72-83%) upon irradiation of neat reactants [93],... 

The preparation of 1,3-dialkylimidazolium halides by conventional heating in solvent under reflux requires several hours to afford reasonable yields and also uses a large excess of alkyl halides and/or organic solvents as the reaction medium. To circumvent these problems Varma and coworkers [106] investigated the preparation of a series of ionic liquids 72 (Scheme 8.74), using microwave irradiation as the energy source, by simple exposure of neat reactants, in open containers, to microwaves by use of an unmodified household MW oven (240 W). 

Fig. 2.7 Fluorous phase catalytic hydroboration. The procedure involves stirring the catalyst (0.1 mol%) in the fluorous phase with neat reactants at 40-45 °C, the cooling on completion of reaction and extracing with THF.

Another problem is the very high concentrations of reactants present in the low-conversion region. The correct derivation of any rate expression such as Eqs. 2-20 and 2-22 requires the use of activities instead of concentrations. The use of concentrations instead of activities assumes a direct proportionality between concentration and activity. This assumption is usually valid at the dilute and moderate concentrations where kinetic studies on small molecules are typically performed. However, the assumption often fails at high concentrations and those are the reaction conditions for the typical step polymerization that proceeds with neat reactants. A related problem is that neither concentration nor activity may be the appropriate measure of the ability of the reaction system to donate a proton to the carboxyl group. The acidity function ho is often the more appropriate measure of acidity for nonaqueous systems or systems containing high acid concentrations [Ritchie, 1990]. Unfortunately, the appropriate ho values are not available for polymerization systems. 

The chemical potential of a solute in equilibrium with its solid or liquid phase is equal to the chemical potential of the neat compound. It is therefore hardly surprising that some papers claiming to report on on water chemistry merely report reactivity comparable to reactivity of the neat reactants. In the author s opinion, the term on water chemistry would preferably be reserved for those processes for which additional rate-enhancing effects are found. 

New developments in microwave-accelerated solventless organic syntheses are appearing in the literature. This expeditious and solvent-free approach involves the exposure of neat reactants to microwave irradiation in conjunction with the use of supported reagents or catalysts which are primarily of mineral origin (Varma, 1999). 

The simplest solvent-free method involves irradiation of neat reactants in an open container. In the absence of reagents or supports, the scope for such processes appears to be limited to relatively straightforward condensations that can be conducted without added catalysts, or to intramolecular thermolytic processes such as rearrangement or elimination. 

Solvent-free conditions can be employed according to three main methods (a) using only neat reactants (b) reactants adsorbed onto solid supports or (c) reactants in the presence of phase transfer catalysts (in the case of anionic reactions). Besides the apparent potential benefits in solvent usage, reactions can be conducted conveniently and rapidly, often without temperature measurement in domestic microwave ovens. However, they now are often carried out under more precisely controlled conditions using monomode reactors initially introduced by the former French manufacturer Prolabo. Nowadays, several systems are available that provide facilities for the accurate measurement and monitoring of temperature throughout the reaction by modulation of emitted power with an infrared detector or an optical fibre. 

Ethyl 3-aminopicolinate (29) with diethyl malonate gave 4-hydroxy-1,5-naphthyridin-2( l //)-one (30) [neat reactants, 120°C, 5 h solid, EtONa, EtOH, reflux, 5h solid, 2.5M NaOH, reflux until gas ceased 96%].1151... 

Somewhat similarly, 3-aminopicolinic acid with ethyl acetoacetate gave 2-methyl-l,5-naphthyridin-4(l//)-one (neat reactants, reflux, 4 h 13%).1000 3-Amino-2-pyridinecarbonitrile (31) with diethyl malonate gave 4-amino-1,5-naphthyridin-2(l//)-one (32) (neat reactants, EtONa, reflux, 7.5 h 36%).725... 

C-Cyano-C-[A-(dimethylaminomethylene) carbamoly methylene -1 -methyl-piperidine (34) gave l-methyl-7-oxo-l,2,3,4,6,7-hexahydro-l,6-naphthyri-dine-8-carbonitrile (35) (neat reactants, 140°C, 20 min >95%).845... 

Methylbenzo-1,4-thiazin-3(4//)-imine hydrochloride (132) with acetic anhydride gave the hexacyclic product (133) (neat reactants, reflux, 90 min 57%), which underwent desulfurization by Raney nickel to afford 4,5-dimethyl-2,7-bis(/V-methylanilino)-1,6-naphthyridine (134) (PhH, reflux, 12 h 20%).1032... 

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