Halogen free synthesis

Scheme 7 Halogen free synthesis of phosphonium ionic liquids...

Another very interesting example from the same group is the use of Sn-Beta for the synthesis of melonal (2,6-dimethyl-5-hepten-l-al), a fragrance that is produced industrially by a Darzens reaction from 6-methyl-5-hepten-2-one, with ethyl chlor-oacetate as reagent. A novel halogen-free synthesis involves the chemoselective... 

Halogen-mediated synthesis of cyclic peroxides through free radical... 

A recent halogen-free benzofuran that shares many structural features with its predecessor shows activity in controlling arrythmias. The synthesis starts with an unusual scheme for building the furan ring. Reaction of the benzyl bromide (2-1) with triphenylphosphine leads to phosphonium salt (2-2). Treatment of the salt with valeryl chloride in the presence of pyridine results in acylation on the now highly activated benzylic carbon (2-3). That product cyclizes to the benzofuran (2-4) on heating with expulsion of triphenylphosphine. Friedel-Crafts acylation of (2-4) with anisoyl chloride in the presence of stannic chloride proceeds on the... 

With respect to the synthesis from amines, C02 and alkyl halides, the synthesis of carbamates from amines, C02 and alcohols (Equation 6.10) is not only a phosgene-free, but also a halogen-free process. Moreover, water forms as the only reaction coproduct. Whilst these features make the route very attractive from the point of view of environmental sustainability, unfortunately the reaction suffers from both thermodynamic and kinetics limitations. Kinetic impediments make necessary the use of a suitable catalyst which, moreover, must be water-tolerant in order to avoid deactivation by cogenerated H20. Several strategies have been explored to overcome these restraints, based mainly on the use of alcohols in a dehydrated form (for instance, as ortho esters or ortho carbonates) [63], or on the use of dehydrating agents [64, 65]. 

Peter W, Roy V H, Andreas B N. Halogen-free ionic hquids-synthesis, properties, and applications. Molten salts XIII. Electrochemical society series. 2002. 19, 147-154. 

The use of palladium and ruthenium as halogen-free carbonylation catalysts has been studied intensively by Shell. The catalysts were principally designed for the carbonylation of olefins in the presence of alcohols in order to yield carboxylic esters [26], but work also well for the synthesis of carboxylic acids or anhydrides. The latter are formed when the reaction is conducted in an acid as a solvent [27]. The palladium systems typically consist of palladium acetate, tertiary phosphines, and strong acids such as mineral acids or acids with weak or noncoordinating anions such as p-toluenesulfonic acid. Remarkable activities are achieved when aromatic phosphines that carry pyridines as substituents are... 

Direct synthesis of sulfur based ionic liquids has been developed as a useful synthetic method for halogen free ionic liquids. The synthesis of sulfur based ionic liquids can generally be split in to two sections (1) sulphonate and (2) sulphate based ionic liquids (Scheme 9). The sulphate based salts are more common than the sulphonates. 

Monocyclic l-acetoxy-2,2-difluorocyclopropane reacted in the same way with cleavage of the bond that linked the acetoxy-substituted carbon with the halogen-free carbon. " This reaction has been applied to the synthesis of side-chain-fluorinated cholesterol derivatives, such as 32 and 33. ... 

It is interesting to note that all the modified alkyl sulfate ionic liquids obtained with these alcohols show attractively low viscosities and their melting points were all below 0 °C. Thus, this synthesis sequence created a new class of halogen-free ionic liquids with attractive physicochemical properties. No organic solvent is needed in... 

The primary particle size of PVF obtained from synthesis decreases as the amount of halogen-free surfactant increases in the aqneous medinm. This is believed to occur because the number of micelles formed by the halogen-free surfactant increases with concentration, providing more nucleation sites for vinyl fluoride polymer particles. This increase in nucleation sites results in smaller particles that are colloidally more stable. As a result, higher solids dispersions can be prepared. ... 

Halogen-mediated syntheses of oxazoles were also described for instance, the iterative bromination/debromination of 126 with NBS allowed a wide-scope, metal- and catalyst-free synthesis of oxazoles 127 (13EJ04554). 

C. M. Jiao, Z. Z. Wang, X. L. Chen, and Y. Hu, Synthesis of a magnesium/ aluminum/iron layered double hydroxide and its flammability characteristics in halogen-free, flame-retardant ethylene/vinyl acetate copolymer composites. Journal of Applied Polymer Science, 107 (2007), 2626-31. 

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