Olefins argentation

The argentation of olefins at 25° is more nearly complete than is the argentation of aromatic hydrocarbons and also differs in that alkyl substituents decrease rather than increase the stability of the com-... 

The alkynes are bonded in essentially the same way as, but less firmly than, the olefins (see Section III,R). In the hex-3-yne series, substitution of an a-hydrogen atom by a methyl group reduces the argentation constant (a measure of the silver-alkyne bond strength) by a factor of roughly 1 /3 this influence of methyl substitution on complex formation is opposite to that observed in the platinum(II) complexes (see Section IV,J). 

Metal Ion-Solute. Transition metals have been loaded onto classical LC columns and used for selective separations (21). More recently successful attempts have been made to control selectivity by metal additions directly to the mobile phase (22). This is a form of ion pairing, but the pairing agent is polar instead of hydrophobic. Silver ion has been used for the separation of olefins (23). M. deRuyter and A. deLeenheer have employed argentation chromatography to resolve difficult mixtures of Retinyl esters (24). 

Also in the 1930s, detailed studies about the thermodynamic stability of adducts of silver(I) with olefins were carried out by Howard Lucas and coworkers, who determined the equilibrium constants between the hydrated Ag+ ion and the corresponding cationic olefin silver(I) complex in dilute aqueous solutions of silver nitrate [25]. In the context of this work, Saul Winstein and Lucas made an initial attempt to describe the interaction between Ag+ and an olefin by quantum mechanics [26]. Assisted by Linus Pauling, they explained the existence of olefin silver(I) compounds in terms of resonance stabilization between the mesomeric forms shown in Fig. 7.4. Following this idea, Kenneth Pitzer proposed a side-on coordination of Ag+ to the olefin in 1945 and explained the stability of the corresponding 1 1 adducts as due to an argentated double bond , in analogy to his concept of the protonated double bond [27]. He postulated that the unoccupied s-orbital of silver(l) allowed the formation of a bond with the olefin, similar to the s-orbital of the proton. 

Addition of acetone to terminal alkenes. Acetone undergoes anti-Markowni-koff addition to terminal olefins in the presence of argentic oxide. Straight-chain alkyl methyl ketones are formed in 73-83% yields. Internal olefins undergo... 

The most popular mobile phases used in argentation HPLC have been mixtures of chloroform (80-90%) and acetic acid <0.5%) with varying proportions of acetonitrile and/or methanol to optimally adjust chromatographic retention. Addition of methanol to the mobile phase is thought to reduce interactions with polar groups on the stationary phase (Powell, 1982) while acetonitrile reduces retention by direct interaction with silver ions bound to the stationary phase, thereby reducing interactions with the olefinic unsaturated bonds (Merritt and Bronson, 1977). Adjustment of the composition of the mobile phase allows the specific types of interactions between the mobile phase, sample molecules and stationary phase to be enhanced or reduced in this way an optimal chromatographic separation can be achieved. 

Reference may be made here to a procedure for separating mixtures of mono-olefinic fatty acids and for subsequently determining the structure of the components [11]. This method utilises two-dimensional TLC on silica gel, impregnated with paraffin and silver nitrate a similar procedure is described in [225]. A scheme for determination of the position and configuration of the double bonds in polyolefinic acids [170] depends on partial hydrogenation with hydrazine, separation of the reduction products through argentation-TLC and determination of... 

Corma, A., Serra, J.M., Serna, P., Valero, S., Argente, E. and Botti, V. (2005). Optimization of olefin epoxidation catalysts applying high-throughput techniques and genetic algorithms assisted by artificial neural networks. J. Catal. 229, 2, 513-524. 

The lOO.OOOg supernatant obtained from the extract showed a diterpene cyciase activity. The resulting olefinic product was identified by radio-GLC and argentation liquid chromatography. This compound has the same retention time on GC, as weli as on silice-sllver nitrate column, as 7,13-abietadiene (standard marker synthesized by reduction of abietic acid). 

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