Retention cyano groups

Silica has often been modified with silver for argentation chromatography because of the additional selectivity conferred by the interactions between silver and Jt-bonds of unsaturated hydrocarbons. In a recent example, methyl linoleate was separated from methyl linolenate on silver-modified silica in a dioxane-hexane mixture.23 Bonded phases using amino or cyano groups have proved to be of great utility. In a recent application on a 250 x 1-mm Deltabond (Keystone Scientific Belief onte, PA) Cyano cyanopropyl column, carbon dioxide was dissolved under pressure into the hexane mobile phase, serving to reduce the viscosity from 6.2 to 1 MPa and improve efficiency and peak symmetry.24 It was proposed that the carbon dioxide served to suppress the effect of residual surface silanols on retention. 

The stereochemistry of alkylation in 2-cyano-6-alkylpiperidines is controlled by the substituent on nitrogen. When the N-substituent is a group such as phenyl or benzyl, such as in Wbenzylpiperidine 273, alkylation gives predominantly the 2,6-cA-dialkyl product 274, with retention of stereochemistry with regard to the cyano group (Equation 27). However, when the N-substituent is a carbamate, such as in t/-butoxycarbonylpiperidine 275, alkylation results in the formation of the 2,6-/ra r-dialkyl product 276 (Equation 28) <2005T3371>. 

The retention times are 8.2 min for [Cl-(CH2)3]g(SiOi 5)5, 16.0 min for [Cl-(CH2)3],o(SiOi 5)10 and 37.4 min for [Cl-(CH2)3]i2(SiOi 5)12 at 7 mL min flow rate. The substitution of the chlorine atoms at octa [(3-chloropropyl)-silsesquioxane] by acetoxy- or cyano groups is possible by using potassium acetate or sodium cyanide and 18-crown-6 as phase transfer catalyst in acetonitrile. In addition to the observed substitution, partial rearrangement to the greater deca- and dodeca-silsesquioxane cages, also took place. 

Whereas the rates of exchange (kex) and racemization (krac) for 2-methyl-3,3-diphcnyl-propanenitrile (k /krac 1.8)142 and phenyl 2,2-diphenylcyclopropyl ketone (kc /krac l)u3 144 are approximately equal in each case (total racemization), 2,2-diphenylcyclo-propanecarbonitrile (kC t./kraCi 12)145 preserves its optical activity with more than 99.9% retention. This finding confirms that the acidifying character of the cyano group is mainly inductive in nature, i.e., the anion retains its pyramidal structure. 

The above results demonstrated the possibility of the quantitative analysis of retention times in reversed-phase liquid chromatography. In addition, a cyano-group-bonded silicone phase was constructed, and MI energy values were calculated. The sum of the MIFS and cnMIES (cyano phase) energies... 

Aminolactols from lactones Retention of cyano groups... 

Cuprous cyanide (s. a. under EtMgBr) Replacement of bromine by cyano groups and chlorine Retention of configuration... 

The addition of primary phosphines to activated alkynes proceeds in the presence of KOH (Scheme 4.288) [451]. Representative substrates included several primary phosphines and a number of cyanoacetylenes. For the vast majority of examples, the conditions were mild, and moderate to excellent yields of the addition products were obtained. The addition reaction was regioselective for the addition of beta to the cyano group and stereoselective for the formation of the Z-isomer. While the addition of secondary phosphines to activated alkynes proceeded without the addition of a catalyst, no reaction was observed with the primary phosphines without the addition of the potassium hydroxide. The authors expanded upon this observation to investigate the addition of secondary phosphines to activated propargyl alcohols. In the absence of added bases, the addition reaction proceeded to generate the vinylphosphine in excellent yield with retention of the alcohol moiety. The regioselectivity and stereochemistry were the same in these reactions and resulted in the formation of Z-isomers. The authors have also reported the addition of... 

Cyano groups (s. a. under Replacement) retention 20, 124 suppl. 21 hydrogenation with - 22, 61 2-Cyano-O-heterocyclics... 

Scheme 9 Organic transformations of the cyano group in the chelated diphosphine products with retention of stereochemistry...

Variations in retention and selectivity have been studied in cyano, phenyl, and octyl reversed bonded phase HPLC columns. The retention of toluene, phenol, aniline, and nitrobenzene in these columns has been measured using binary mixtures of water and methanol, acetonitrile, or tetrahydrofuran mobile phases in order to determine the relative contributions of proton donor-proton acceptor and dipole-dipole interactions in the retention process. Retention and selectivity in these columns were correlated with polar group selectivities of mobile-phase organic modifiers and the polarity of the bonded stationary phases. In spite of the prominent role of bonded phase volume and residual silanols in the retention process, each column exhibited some unique selectivities when used with different organic modifiers [84],... 

Cyano or nitrile phases are prepared by the reaction of silica with 3-cyanopropyl silane. They are also polar with weak retention in RPC. It is difficult to determine whether the polar interaction of this phase is caused by the dipole of the nitrile group or by residual silanols. There is a lack of significant studies of retention mechanisms with this phase. 

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