Reactions expansion processes

Whilst sodium bicarbonate is the primary blowing agent, it is common compounding practice to use it in conjunction with a proportion of a weak acid, such as stearic or oleic acid, whose function is to trigger the reaction and assist in the uniform decomposition of the bicarbonate. The higher than normal fatty acid level will also act as a process aid, facilitating the bubble expansion process. 

The reaction of vinylcarbenoids with vinyl ethers can lead to other types of [3 + 2] cycloadditions. The symmetric synthesis of 2,3-dihydrofurans is readily achieved by reaction of rhodium-stabilized vinylcarbenoids with vinyl ethers (Scheme 14.17) [107]. In this case, (J )-pantolactone is used as a chiral auxihary. The initial cyclopropanation proceeds with high asymmetric induction upon deprotection of the silyl enol ether 146, ring expansion occurs to furnish the dihydrofuran 147, with no significant epi-merization during the ring-expansion process. 

A Study of Combustion and Recombination Reactions During the Nozzle Expansion Process of a Liquid Propellent Rocket Engine , Ibid, pp 366-74 F2) W.E. Johnson W. 

In this chapter, the recent advances in amidocarbonylations, cyclohydrocarbonylations, aminocarbonylations, cascade carbonylative cyclizations, carbonylative ring-expansion reactions, thiocarbonylations, and related reactions are reviewed and the scope and mechanisms of these reactions are discussed. It is clear that these carbonylation reactions play important roles in synthetic organic chemistry as well as organometallic chemistry. Some of the reactions have already been used in industrial processes and many others have high potential to become commercial processes in the future. The use of microwave irradiation and substitutes of carbon monoxide has made carbonylation processes suitable for combinatorial chemistry and laboratory syntheses without using carbon monoxide gas. The use of non-conventional reaction media such as SCCO2 and ionic liquids makes product separation and catalyst recovery/reuse easier. Thus, these processes can be operated in an environmentally friendly manner. Judging from the innovative developments in various carbonylations in the last decade, it is easy to anticipate that newer and creative advances will be made in the next decade in carbonylation reactions and processes. 

Aminotropones have been reported through a single-step cyclization-ring expansion process from 4-aminocyclohexa-2,5-dienones (p-quinamines) bearing a 4-sulfinyl or 4-sulfonyl methyl group on reaction with sodium hydride (Scheme 62).97... 

It should be noted that in the polyhedral expansion process, as idealized in Eqs. (5) and (6), the product mctallocarborane has one more vertex than was present in the carborane starting material—hence the origin of the descriptive phrase polyhedral expansion. By contrast, wThen metallocarboranes are prepared by reaction with O2B9H112- ions, which are prepared from the icosahedral C2B10H12 carboranes, twelve-vertex metallocarboranes result. 

Mechanistically, the Beirut reaction is a heterocycle expansion-process where the nucleophile attack conducts, after atomic rearrangements, to a new diazine system. In general, a further elimination—i.e., of H2O, amines, acetate—aromatizes the new heterocycle. 

If the reaction times taking place in the reacting mixture are extremely fast compared to the expansion time, then chemical equilibrium will be maintained at all instances during the expansion process this flow process is referred to as eauili- brium flow. However, expansion in the nozzle may occur so rapidly that the reactions may not be fast enough to maintain equilibrium. In fact the expansion can be... 

Radical reactions are looked upon by many chemists as uncontrollable processes which yield intractable mixtures of products. Even so, the ingenuity of synthetic chemists has resulted in many useful synthetic schemes via radical pathways. These include chain lengthening, ring formation and ring expansion processes. This synthetic work has seen dramatic steps forward over the last few decades and has been the subject of several general reviews recently664"669. Other notable reviews have also been written10,11,61,670 which cover more specific aspects of radical reactions and the reader is referred to all these sources for further and in-depth information. 

In this section, the subject is subdivided into three parts. These are, first, chain lengthening reactions, second, cyclizations and last, ring expansion processes. These processes may be either chain or nonchain reactions. However, in this review, only the more common chain reactions will be discussed. The reader is referred to the reviews of Curran665 667,669 for details about the less common nonchain processes, and to the chapter by J. Green concerning metal-mediated reactions of halides in the present volume. 

Lastly, in a very similar ring expansion process, bicyclic compounds, formed by reaction of mono- or dihalocarbenes with cyclohexanone enols, undergo ring expansion to give cyclohexenones (equation 194)1015-1017. 

Scheme VI/7. The transamidation reaction as a repeatable ring expansion process [30].

Many industrial processes require accurate environmental control. Examples include chemical reactions and processes that are affected by atmospheric conditions biochemical reactions quality, uniformity, and standardization of certain products factors such as rate of crystallization and size of crystals product moisture content or regain deliquescence, lumping, and caking of hygroscopic materials expansion and contraction of macliines and products physical, chemical, and biological cleanliness effects of static electricity odors and fumes conditions in storage and packaging quality of painted and lacquered finishes simulation of stratosphere or space conditions and productivity and comf ort of workers. Controlled atmospheric conditions are... 

A curious reaction was observed when epoxy derivatives of certain exo-methylene groups e.g. i) were treated with BFs or perchloric acid [34,35]. The products are believed to be five-membered cycHc ethers 2.). The exact mechanism of the ring expansion process is uncertain, but it has been represented as epoxide cleavage concerted with two stereospecific hydride... 

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