Dakin-West reaction


A special application of heteroaromatic acylation via a modified Dakin-West reaction leads to a-fluoro ketone derivatives [50] (equation 30) Such fluoro ketones have been successfully used as enzyme inhibitors in modern bioorganic chemistry [5, 6]  [c.535]

AH of these processes are operated in conventional glass-lined or stainless steel kettles or reactors. The pressure rating of the reactors depends on the volatility of the monomers used. In the homopolymerization of the vinyl acetate and its copolymerization with monomers of low vapor pressure, the use of vessels with a pressure rating close to atmospheric pressure is sufficient. The ethylene—vinyl acetate copolymer (EVA) processes must of necessity be operated under high pressure (40). Agitation design in these systems is important, taking into consideration the need to blend all the ingredients without zones of high concentration and remove the heat from the reaction mass while a voiding subjecting the reaction mixture to conditions of high shear which could destabilize the material. Heat removal in atmospheric pressure reactions, especially those carried out close to or higher than the boiling point of the vinyl acetate uses reflux condensers. In vinyl acetate polymerizations where low temperatures are maintained to avoid chain transfer, which results in lowering the average molecular weight, internal coils, jackets on the reactors, and external heat exchangers are used.  [c.464]

Control of the process is important to ensure reproducibiUty of the product. Methods have been developed to control the composition of copolymers and their molecular weight (53,54). Calorimetric methods have been described to estimate conversion and provide the basis for control of the reaction. Other properties such as density and particle size can also be monitored to gauge the reaction progress and development of the product properties (55—57). Agitator design is important in controlling particle size and can influence the kinetics, molecular weight, and coagulum formation (58).  [c.464]

High performance polyurethane elastomers are used in conformal coating, potting, and in reactive injection mol ding (or reaction impingement mol ding) of IC devices. Furthermore, rigid polyurethane foams, most often in free-foam densities of 128—288 kg/m [8—18 Ibs/ft (pcf)]> useful for embedding complex electronic systems. The encapsulant is injected or poured as a Hquid into the cavity containing the electronics. As the polymerisation reactions occur, a side-reaction with water produces small bubbles and causes the urethane to foam. Usually within two minutes, the rising foam is locked into position by the cure advancement. With proper design, the rising foam pushes air out of the cavity, giving a void-free encapsulant. These materials offer weight reduction, relatively good dielectric properties, and protection from shock. They are used in a number of military ordnance systems at up to 27,000 -forces.  [c.190]

We have seen in this and other books many complicated analysis methods as well as some involved design methods for composite structures. An immediate reaction might be that those analysis and design methods are overly involved and indeed intimidating. Some of the methods are so complicated, and there are so many behavioral aspects to take into consideration, that we have a difficult time trying to take account of all pertinent factors. We have, though, some very fundamental objectives in structural design. We know that we have some very attractive properties to deal with when we intend to use or consider composite materials for structural applications. We know that if we use those properties correctly, we can build structures which, with composite materials, have lower weight, or higher strength and stiffness, and generally higher performance indexes than with metals. We want to achieve those objectives, yet some significant problem areas or concerns exist. We will address those problem areas one-by-one and offer some recommendations for effective composite structures design. Much of the discussion in this section is patterned after the theme of a very insightful  [c.453]

We have seen in this and other books many complicated analysis methods as well as some involved design methods for composite structures. An immediate reaction might be that those analysis and design methods are overly involved and indeed intimidating. Some of the methods are so complicated, and there are so many behavioral aspects to take into consideration, that we have a difficult time trying to take account of all pertinent factors. We have, though, some very fundamental objectives in structural design. We know that we have some very attractive properties to deal with when we intend to use or consider composite materials for structural applications. We know that if we use those properties correctly, we can build structures which, with composite materials, have lower weight, or higher strength and stiffness, and generally higher performance indexes than with metals. We want to achieve those objectives, yet some significant problem areas or concerns exist. We will address those problem areas one-by-one and offer some recommendations for effective composite structures design. Much of the discussion in this section is patterned after the theme of a very insightful  [c.453]

It may be mentioned that diazonium fluoborates containing the nitro group usually decompose suddenly and with violence upon heating, hence if o- or p-fluonitrobenzene are required, the fluoborates (in 10-20 g. quantities) should he mixed with 3-4 times their weight of pure dry sand (or barium sulphate or sodium fluoride) and heated cautiously until decomposition commences intermittent heating will be required to complete the reaction.  [c.595]

In the meantime, prepare a sodium sulphite solution as follows. In a 2-litre beaker or bolt-head flask place 50 g. of sodium hydroxide (2) and add 500 ml. of water. When the sodium hydroxide has dissolved, add 112-5 g. of recrystallised sodium bisulphite (3), and stir mechanically until the solid has dissolved. Cool the resulting solution to about 25° and add a few drops of phenolphthalein indicator solution. Introduce small quantities of sodium bisulphite until the pink colour of the solution just disappears, then stir in a further 12 g. of sodium bisulphite (the total weight required should not exceed 135-140 g.). Cool this solution, with stirring, to about 5° by immersion in an ice bath, then add about 60 g. of crushed ice. Run in the ice-cold diazonium solution as rapidly as possible, while stirring vigorously. The reaction mixture immediately acquires a bright orange-red colour. Slowly heat the solution to 60-70 on a water bath and maintain this temperature for 30-60 minutes, i.e., until the colour becomes quite dark. Acidify the solution to litmus with concentrated hydrochloric acid (40-50 ml. are required) continue the heating on a boiling water bath until the colour becomes much hghter and in any case for 4-6 hours. If any solid is present, filter the solution. To the hot, clear solution add, with stirring, 500 ml. of concentrated hydrochloric acid cool, first in running water, and then in a freezing mixture to 0°. The phenylhydrazine hydrochloride separates as yellowish or pinkish crystals. CoUect them on a Buchner funnel, drain, wash with 25 ml. of dilute hydrochloric acid (1 3), and press well with a large glass stopper (4).  [c.636]

Diazotizations ia organic solvents foUowed by coupling or simultaneous diazotization and coupling ia one step have gained importance (13). The process can be conducted batchwise or continuously. When the dye is soluble ia the reaction mixture, the product can be packed out ia its entirety. This offers an advantage ia reduciag the loss of dye duriag processiag. The Hquid dye also offers ease of handling, accuracy of measurement, and uniformity. Besides sodium nitrite [7632-00-0] and nitrosylsulfuric acid, nitrites of glycol and glycol derivatives (14) can be employed as diazotiziag agents. These compounds ia comparison to nitrites of low molecular weight alcohols, such as amyl nitrite, are much less dangerous ia handling, physiological properties, and explosiveness. These types of processes have been employed for a limited number of commercial azo dyes. The mechanism of the diazotization reaction has appeared (15) and other results have been reviewed (16,17). Nitrosation of the amino group is the rate determining step transformation to the diazonium ion foUows  [c.426]


See pages that mention the term Dakin-West reaction : [c.593]    [c.81]    [c.224]   
Chemistry of Organic Fluorine compounds II (1995) -- [ c.535 , c.538 ]