Phosphor oligomers

Results from infrared spectroscopy indicate that the only species present in 50 % phosphoric acid are H3PO4, HjPOj and their oligomers (Wilson Mesley, 1968). There is evidence that HgPjOg, the phosphoric acid dimer, and HsPjOg, the triple ion H2PO4.. HjPOj, are also present (Elmore,... 

Cyclizations can also be carried out with an esterified oligomer of phosphoric acid called polyphosphate ester, which is chloroform soluble.55 Another reagent of this type is trimethylsilyl polyphosphate (Scheme 11.4, Entry 13).56 Neat methanesul-fonic acid is also an effective reagent for intramolecular Friedel-Crafts acylation (Scheme 11.4, Entry 14).57... 

Imidazolides of adenylic acid (ImpA) or uridylic acid (ImpU) are polycondensed to oligonucleotides by means of Zn2+ ions. 1673 The resulting phosphordiester bond was found to be of the 2, 5 type. In the reaction of nucleoside 5 -phosphoric acid methyl ester with ImpA in the presence of MgC, 2, 5 -dinucleotides are formed six to nine times more frequently than the corresponding 3, 5 compounds. 63 Polycondensations of ImpA in aqueous solution in the presence of various divalent metal ions lead to short oligo-adenylic acids (pA) (n = 1—5) mainly with 2, 5 -intemucleotide linkages. With Pb2+, for example, the total yield of oligomers was as high as 57%. 1683 1693... 

Condensation of the 5 -phosphoric imidazolide of adenosine (ImpA) with itself and P yP -diadenosine 5, 5 -phyrophosphate (AppA) in water in the presence of Na -mont-morillonite clay leads mainly to 3, 5 -linked oligomers. These results are discussed in the context of the potential importance of mineral catalysts to the formation of RNA on the... 

The transportation fuels produced and marketed (Table 18.9)40 met the South African fuel specifications of that time and included some coal-derived liquids (not shown in Figure 18.5). Although the refinery originally produced no jet fuel, it was demonstrated that the hydrogenated kerosene range oligomers from olefin oligomerization over a solid phosphoric acid catalyst met the requirements for jet fuel.38 (Semisynthetic jet fuel was approved in 1999 and fully synthetic jet fuel was approved in 2008 DEFSTAN 91-91/Issue 6). 

Figure 2.9 Inductively coupled plasma detection of diaminodichloroplatinum(n). Conditions column, Shodex OH, 25 cm x 4.1 mm i.d. eluent, 0.01 m phosphoric acid flow rate, 1 ml min-1 detector, emission at platinum line 265.9 nm. Samples cis and trans diaminodichloroplatinums. The second peaks are considered to be their oligomers.

Martens et a/. 3S showed that HZSM-22 synthesized in a pure form with controlled crystal size is a promising catalyst for the oligomerization of propene to Q-C12 olefins. It was found that the reaction occurs at or near the outer surface and the products formed are mainly dimers. In addition, an increase of the linearity of the oligomers as compared with HZSM-5 or solid phosphoric acid was found. It was tentatively proposed that active sites located at the pore mouths are responsible for this shape selective effect. 

The stereoelectronic effect of the RO-group is less pronounced, when bulkier electrophiles are employed (Table 3, entries 23,27,28), but is increased when the well solvating agent hexamethyl phosphorous amide (HMPA) is used as an additive 61,68). On the other hand, if one performs the deprotonation/alkylation sequence in the unpolar solvent pentane, a complete reversal of the stereochemical outcome provides the coproduct in excess (Eq. 35)61 Now a coordination of the lithium cation to the siloxy function might favour structures like 109 (or its oligomers) and cause predominant formation of cO-cyclopropanes. 

The Fischer indole synthesis itself is catalysed in this case by polyphosphoric acid (PPA), a sticky gum based on phosphoric acid (H3PO4) but dehydrated so that it contains some oligomers. It is often used as a catalyst in organic reactions and residues are easily removed in water. 

Compositions of three types of carrier ampholytes. Short segments of some representative carrier ampholytes are shown. The different types of molecules arise from different manufacturing processes. Most carrier ampholytes are mixtures of oligomers (about 300- 1000 Da in size) containing multiple aliphatic amino and carboxylate groups (A and B), although some types contain sulfonic and phosphoric acid residues (C). See Ref. I. 

Nucleic acids in which various purine and pyrimidine bases are united by bridges of D-2-deoxyribose or D-2-ribose phosphoric acid play vital roles in the metabolism of living cells.179 Many oligonucleotides (which are heterocyclic co-oligomers) have been synthesized in studying the biochemistry of nucleic acids.180... 

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