Direct Route

The alkylation reaction of various alkali and alkaline-earth metal carbonates with alkyl halides R(CH2)nX (X = Cl, Br, I) is a primary synthetic procedure in organic chemistry for obtaining various symmetrical and unsymmetrical dialkyl carbonates under phase-transfer conditions in polar aprotic solvents [45]. Excellent yields may be obtained by running the reaction at 383 K in ionic liquids such as 

With soluble catalysts, both experimental investigations and density functional theory (DFT) calculations with a soluble Nb(OCH3)5 catalyst [66, 94] support the 

The transformation of A to B to C underlines an increase in the nuclearity of the resting species with the formation of Sn-O-Sn linkages, the tin centers being pentacoordinated. It is worth noting that monomeric species are most likely involved in the catalytic cycle. 

Although the direct C02-based route to dialkyl carbonates offers selectivity improvement (almost 100% for DMC synthesis), limited yields may result due to unfavorable thermodynamics and catalyst deactivation by water. Until now, mechanistic studies have been fruitful in identifying some of the key steps of the 

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A sequence of successive con figurations from a Mon te Carlo simulation constitutes a trajectory in phase space with IlypcrC hem. this trajectory in ay be saved and played back in the same way as a dynamics trajectory. With appropriate choices of setup parameters, the Mon te Carlo m ethod m ay ach leve ec nilibration more rapidly than molecular dynamics. Tor some systems, then. Monte C arlo provides a more direct route to equilibrium sinictural and thermodynamic properties. However, these calculations can be quite long, depentiing upon the system studied. 

Tetrafluoropyrimidine has been prepared by direct fluoriaation of 2,4,6-trifluoropyriniidine with silver difluoride ia perfluorobutylamiae solveat (461,462). A more direct route (85% yield) is the reactioa of tetrachloropyriaiidiae and potassium fluoride ia an autoclave at 480°C for 42 h (463). 

As capital costs increase, operating costs decrease, as shown in Table 13 those costs involved in the production of HCl by various routes are presented in Table 13 for some nominal production capacities. These data indicate the direct route from 2 most economic among all the... 

Vapor-phase catalytic oxidation of dutene is a mote direct route to the dianhydtide. Hbls in Europe apparently uses this route, which eliminates the need for a separate dehydration step and for handling of any oxidants or solvents. Continuous operation is faciHtated, corrosion is minimized, and product recovery is simplified. The vapor-phase oxidation of dutene is similar to that of o-xylene to phthaHc anhydtide, and phthaHc anhydtide units can be... 

Ethanol s use as a chemical iatemiediate (Table 8) suffered considerably from its replacement ia the production of acetaldehyde, butyraldehyde, acetic acid, and ethyUiexanol. The switch from the ethanol route to those products has depressed demand for ethanol by more than 300 x 10 L (80 x 10 gal) siace 1970. This decrease reflects newer technologies for the manufacture of acetaldehyde and acetic acid, which is the largest use for acetaldehyde, by direct routes usiag ethylene, butane (173), and methanol. Oxo processes (qv) such as Union Carbide s Low Pressure Oxo process for the production of butanol and ethyUiexanol have totaUy replaced the processes based on acetaldehyde. For example, U.S. consumption of ethanol for acetaldehyde manufacture declined steadily from 50% ia 1962 to 37% ia 1964 and none ia 1990. Butadiene was made from ethanol on a large scale duriag World War II, but this route is no longer competitive with butadiene derived from petroleum operations. 

In 1959 a new non-protein L-a-amino acid was isolated from the seeds of Acacia willardiana and later from other species of Acacia-, it proved to be l-/3-amino-/3-carboxyethyluracil (977) (59ZPC(316)164). The structure was confirmed by at least four syntheses in the next few years. The most important involves a Shaw synthesis (Section 2.13.3.1.2e) of the acetal (975) and hydrolysis to the aldyhyde (976) followed by a Strecker reaction (potassium cyanide, ammonia and ammonium chloride) to give DL-willardiine (977) after resolution, the L-isomer was identical with natural material (62JCS583). Although not unambiguous, a Principal Synthesis from the ureido acid (978) and ethyl formylacetate is the most direct route (64ZOB407). 

The procedure described here serves to illustrate a new, general method for effecting the < -arylation of g-dicarbonyl compounds by means of an aryllead triacetate under very mild conditions. Although the first synthesis of an aryllead triacetate was reported relatively recently, a wide range of these compounds can now be readily prepared. The most direct route to these compounds is plumbation of an aromatic compound with lead tetraacetate, and in the procedure reported here p-methoxyphenyllead triacetate has been prepared in this way. It may also be obtained by reaction of the diarylmercury with lead tetraacetate, a longer, but more general method of synthesis of aryllead triacetates. 

Progesterone (81) is dehydrogenated by DDQ in dioxane, with acid catalysis. This method and the chloranil reaction (see section VI-A) provide the most direct route from A -3-ketones to -3-ketones. 

The pure olefin is best prepared via the bromohydrin (131) a more direct route from the tosylate (129) yields a mixture of (132) and its A -isomer. The indirect method is most suitable for preparing A -olefins in the 5jS-series. 

Piping should also be arranged to allow Uie shortest, most direct route without congestion. They should be installed to prevent Uie trapping of liquids and should contain adequate valving and provisions for contracUon and expansion. Joints must be properly welded and secure. 

Molecular electric quadrupole moments are more elusive animals, and they are not particularly easy to determine experimentally. Prior to 1970, the only direct routes to these quantities were from the Kerr and Cotton-Mouton effects. They can now be obtained from microwave Zeeman spectroscopy, to fair accuracy. It is fair to say that direct calculation offers a faster and more reliable route to this property than experiment. 

In 1974, Hegedus and coworkers reported the pa]ladium(II)-promoted addition of secondary amines to a-olefins by analogy to the Wacker oxidation of terminal olefins and the platinum(II) promoted variant described earlier. This transformation provided an early example of (formally) alkene hydroamination and a remarkably direct route to tertiary amines without the usual problems associated with the use of alkyl halide electrophiles. 

A second direct route to an extended 3,4-dihydro-j8-carbolinium system (120) using the Bischler-Napieralski ring closure is based on the cyclization of intermediates of general structure 118. Three approaches to intermediates of this type have been developed in connection with stereospecific syntheses in the indole alkaloid field. The first approach, introduced independently by Stork and Hill and by van Tamelen and co-workers and often used... 

A more direct route to this ring system consists in the treatment of a ketone with an aqueous solution of potassium cya-... 

York City. Despite economic transactions and contractual agreements that would call for a direct route with minimized losses, the path of power flow is dictated by the laws of physics and the system parameters. 

A direct route for acetone from propylene was developed using a homogeneous catalyst similar to Wacker system (PdCl2/CuCl2). The reaction conditions are similar to those used for ethylene oxidation to acetaldehyde. ... 

One of the most direct routes to vinylsilanes uses vinyl halides as starting materials. Metal-halogen exchange, followed by electrophilic attack by TMSC1, can often provide the vinylsilane quickly and in good yield. As an added bonus, vinyl bromides have been shown (10, II) to proceed through this sequence with retention of double-bond stereochemistry. 

The transition metal catalysed addition of a hydridosilane to a multiply-bonded system is known as hydrosilylation (1). Under such conditions, alkynes undergo clear cis-addition, so providing one of the most direct routes to vinylsilanes (Chapter 3). Hydridosilanes also add to the carbonyl group of saturated aldehydes and ketones, to produce alkyl silyl ethers. Fot example, under suitable conditions, 4-t-butylcyclohexanone (2) can be reduced with a high degree of stereoselectivity. 

This procedure has several advantages over previous methods. It provides a simple direct route to unsymmetrically substituted isoxazoles in which the substituents are unequivocally located. The method uses readily available starting materials and can be used for the synthesis of variety of substituted isoxazoles in which the substituents are nonreactive to butyllithium. Examples of products synthesized by this method7 are given in Table I. 

A direct route to obtain polyimides and polybenzoxazoles without diacid has been explored by using direct carbonylation of an aromatic diiodo compound.100 The reactions were performed in polar aprotic solvent. The cheaper chlorine derivative can be used instead of the iodo one when it is located on a strongly... 

The displacement of halogeno by cyano substituents has not been used frequently in the quinoxaline series of late. Such a reaction is often easy in the 2-and 3-positions but somewhat more difficult in the 5-8-positions an alternative indirect route via a trimethylammonioquinoxaline salt is sometimes preferable (see Section 6.3.2.4). The following examples illustrate the direct route. 

The one-pot MCR of methylene active nitriles 47 has been used in the synthesis of both pyrano- and pyrido[2,3-d]pyrimidine-2,4-diones in a single-mode microwave reactor [90]. Microwave irradiation of either barbituric acids 61 or 6-amino- or 6-(hydroxyamino)uracils 62 with triethyl-orthoformate and nitriles 47 (Z = CN, C02Et) with acetic anhydride at 75 °C for 2-8 min gave pyrano- and pyrido[2,3-d]pyrimidines in excellent yield and also provided a direct route to pyrido[2,3-d]pyrimidine N-oxides (Scheme 27). 

Reversible Unimolecular Reactions. The intrinsic reaction steps in heterogeneously catalyzed reactions are usually reversible. The various limiting cases can be found by taking limits before redefining the constants, e.g., take limits on Equation (10.11), not Equation (10.12). However, a more direct route is to assume that the fast steps achieve equilibrium before deriving the counterpart to Equation (10.11). 

The point of the weighting function can be illustrated by considering the two extremes of complete scrambling (for which ) = 1), and complete routing (forwhich f() = 1/Fp). If we choose to make f(F) = F ,we have constructed a convenient function that can be adjusted to take intermediate values (for this particular DIFF), where CO may take any values between 0 (where f(F) = 1 scrambling) and -1 (where f(F) = 1/F direct routing). Later (Section 4) we use an alternative formulation, in which... 

In fact a somewhat wider range of dp and dw values provides a reasonable fit, and what is regarded as the best fit is rather subjective. For example, dp = 5, dp, = 2 gives the best average values, but dp = 4, dN = 3 give the least scatter (but with an offset mean). Furthermore, not all data are consistent (the low protein data seem most difficult to fit). Nevertheless, it is clear that the DIFF gives a reasonable prediction if f() is taken to be close to direct routing dp is +4 or +5%o and dn is +3 to +l%o (and anti-correlated with dp). 

This clearly overstates the potential of demographic study to provide a mechanistic understanding of plant responses to environments and, if implemented, would lead to unnecessary delay in the development of generalising principles. The remainder of this chapter is founded on the assumption that the most direct route to a coherent predictive theory of plant responses to stress is likely to involve a synthesis of insights derived from plant population biology, ecophysiology, and many other fields of botanical endeavour. 

Dream reactions can be performed using chemical micro process engineering, e.g., via direct routes from hazardous elements [18]. The direct fluorination starting from elemental fluorine was performed both on aromatics and aliphatics, avoiding the circuitous Anthraquinone process. While the direct fluorination needs hours in a laboratory bubble column, it is completed within seconds or even milliseconds when using a miniature bubble column. Conversions with the volatile and explosive diazomethane, commonly used for methylation, have been conducted safely as well with micro-reactors in a continuous mode. 

In Australia and Malaysia, which have a federal system of government, the delegation of inspection responsibilities and reporting systems is organized in different ways. In Malaysia, inspection of distribution channels in the states comes under the authority of the State Deputy Director of Health (Pharmacy), and there is a direct route for reporting between the states and the federal agencies. 

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