Basic reagents, Table

The basic reagent scheme used in the concentrators varies and is dependent on the type of copper minerals present in the ore, and the mineral composition of the gangue. The reagent scheme used in the three main concentrators treating this ore type is presented in Table 19.11. 

Compounds which tend to eliminate hydrogen fluoride in the presence of a base are 1.2-difluoroalkancs, oqa -difluoro ethers, a,a -difluoro sulfides, /1-fluorocarbony] compounds, 1,1-diaryl- and 1,2-diarylpolyfluoroalkanes, 277-acyl fluorides and polyfluoroalkylammonium salts. Polyfluoroalkancs (see Table 2) are relatively labile towards basic reagents. If two elimination pathways are possible, such as in 1,1,2.3,3,3-hexafluoropropanc (1), hydrogen is eliminated from the carbon bearing fewer fluorines.11,2... 

Normally, C-H bonds are highly resistant to attack by basic reagents, but removal of a proton alpha to a carbonyl group results in the formation of a considerably stabilized anion with a substantial proportion of the negative charge on oxygen, as represented by the valence-bond structure 1a. Carbonyl compounds such as 2-propanone therefore are weak acids, only slightly weaker than alcohols (compare the pKa values for some representative compounds in Table 17-1).1... 

KF as the best basic reagents and towards DMF as the best solvent. An accurate determination of yields and purity of 9.73 in all reaction vessels selected entry 43 (TEA-DMF) as the best compromise for step a, Fig. 9.29. A similar optimization was performed for the f-butyl ester hydrolysis (step b, Fig. 9.29), creating the 39-member reaction library L19 by permutations of acidic reagents and solvents, and addition of adjuvants (Fig. 9.30). The screening outcome (Table 9.3) highlighted the poor performances of ion-exchange resins (no reaction) and TFA (unclean product) to prepare 9.74, and selected entry 7 (HCl/EtOAc) as the best reaction conditions to obtain clean 9.74 (CSA (camphor sulfonic acid) actually performed slightly better, but the reaction work-up was less automation friendly). The whole manual optimization process required three to four days, and the best reaction conditions were used directly to produce a 590-member discrete library, which met the >75% purity cutoff (78). 

Silyl ethers of hydroxy amino acids have been employed in both solid-phase and solution peptide synthesis. Since the TBDMS and TBDPS ether groups are stable to piperidine and other basic reagents, these derivatives of Ser and Thr (Tables 8 and 9) can be used in the Fmoc strategy.Homodetic peptides and depsipeptides have also been synthesized using TBDMS hydroxy protection for phenyllactic acid and hydroxyisovaleric acid, respectively. 

In the part of this scheme relating to antioxidants he uses acetylated paper and two solvent systems, one for basic and one for phenolic acidic constituents. Identification was based mainly on the Rf value of each constituent and on the colours produced by various spray reagents (Tables 6.1 and 6.2). 

Aldehydes can be protected as N,N-acetals, which are stable to highly basic reagents such as RLi. Therefore, the aldehyde function of 14 was treated with N,N -dimethylethylenediamine to convert it to a N,N-acetal-protected styrene (14e). ° Unlike the oxygen analogues, 14e was anionically polymerized without problem to afford a living polymer, which was stable in THF at -78 °C even after 24 h (Table 3). The protective group was quantitatively removed by acid hydrolysis with 2 N HCl in THF (Scheme 8). The SEC trace of the poly(14) thus obtained... 

The monomethine cyanines with a methyl group on the chain (Table 2113) are prepared in a basic medium from a 2-alkyl-substituted thiazolium by condensation of an electrophilic reagent. 

Basic Lead Acetate. Basic lead acetate [1335-32-6] (lead subacetate), 2Pb(0H)2-Pb(C2H3 02 )2, is a heavy white powder which is used for sugar analyses. Some physical properties are given in Table 4. Reagent grade is available in 11.3-kg cartons and in 45- and 147-kg fiber dmms. 

Table 2. Basicity Factors of Common Alkaline Reagents ...

In this section three main aspects will be considered. Firstly, the basic strengths of the principal heterocyclic systems under review and the effects of structural modification on this parameter will be discussed. For reference some pK values are collected in Table 3. Secondly, the position of protonation in these carbon-protonating systems will be considered. Thirdly, the reactivity aspects of protonation are mentioned. Protonation yields in most cases highly reactive electrophilic species. Under conditions in which both protonated and non-protonated base co-exist, polymerization frequently occurs. Further ipso protonation of substituted derivatives may induce rearrangement, and also the protonated heterocycles are found to be subject to ring-opening attack by nucleophilic reagents. 

Details for the preparation of the solutions referred to in the table are as follows (note that concentrations are expressed in molalities) all reagents must be of the highest purity. Freshly distilled water protected from carbon dioxide during cooling, having a pH of 6.7-7.3, should be used, and is essential for basic standards. De-ionised water is also suitable. Standard buffer solutions may be stored in well-closed Pyrex or polythene bottles. If the formation of mould or sediment is visible the solution must be discarded. 

---