Triethyloxonium salts

O. Nuyken, P. H. Plesch, Binary Ionogenic Equilibria exemplified by Acetyl Hexafluoroantimonate and their Implications for Cationic Polymerisation, Chem. and Ind., 1973, 379. - See also F. R. Jones, P. H. Plesch, The Association Constants of Triethyloxonium Salts and their Solvation by Diethyl Ether, Chem. Comm., 1970, 1018. 

Subsequent experiments by Jones and Plesch [11] showed that polymers of (I) and of 1,3-dioxepan made with various triethyloxonium salts as catalysts, were also almost devoid of end-groups and therefore the great majority of the molecules must also be cyclic. 

As mentioned above, the only quantitative information of this kind which is available relates to polymers made with perchloric acid or triethyloxonium salts. 

The Decomposition of Triethyloxonium Salts, F.R. Jones and P.H. Plesch, Chemical Communications, 1969, 1231-1232. 

Both trimethyl- and triethyloxonium salts are fairly stable and can be isolated as crystalline solids. They are prepared more conveniently from the appropriate boron trifluoride etherate and chloromethyloxacyclopropane (epichloro-hydrin, see Exercise 15-56). 

However, when triethyloxonium salts are used as initiator, cyclic oligomer is also formed. Since in this case no terminal hydroxyl groups are formed, the formation of the tetramer must also be possible by another reaction mechanism. 

The initiation mechanism for cationic polymerization of cyclic ethers, vinyl amines, and alkoxy styrenes has been investigated by A. Ledwith. He used stable cations, like tropylium or triphenylmethyl cations with stable anions, like SbCl6, and distinguished between three initiation reactions cation additions, hydride abstraction, and electron transfer. One of the typical examples of cationic polymerization, in which the propagating species is the oxonium ion, is the polymerization of tetra-hydrofuran. P. and M. P. Dreyfuss studied this polymerization with the triethyloxonium salts of various counterions and established an order of... 

We have chosen to use preformed triethyloxonium salts as initiators. Polymerizations initiated with these salts remain nearly colorless. The... 

The salts used as initiators are all triethyloxonium salts of the formula (C2H5)30+X. The gegenions (X ) examined are BF4 , PF6", SbF6", and SbCl6. The first and last are well-known compounds and have been used frequently. The other two have been mentioned only in the patent literature (5, 6). These four gegenions probably include all the most common ones used in THF polymerizations except the ones resulting from tri-ethylaluminum-water systems (11). In this case the structure of the gegenion is probably complex and has not yet been established. 

Catalysts. The triethyloxonium salts were all prepared by reaction of epichlorohydrin with the Lewis acid corresponding to the desired gegenion in ether. The method of Meerwein et al. (14) was used. They were stored under high vacuum until needed. 

Note that the chemical shifts are very similar for all of these salts, in agreement with their all being triethyloxonium salts supposed. The... 

Reaction of pyridine-N-oxides with triethyloxonium salt in methylene chloride or chloroform gives directly AT-alkoxy pyridinium salts with high yield. Quinolinium salts can also be prepared from the corresponding N-oxides [46], The synthetic procedure does not require the anion exchange reaction since triethyl oxonium salt possesses a non-nucleophilic counter anion, i.e. PFg ... 

Immediately after the start of dioxolane polymerization, initiated by the triethyloxonium salt Et30 + B, the carboxonium centres present are of the form [127]... 

Initiators such as triethyloxonium salts, oxycarbenium salts (e.g., C6H5CO + A ), or dioxolenium salts initiate the polymerization by direct... 

Solvolysis rates of t-butyl-dimethylsulfonium salts decrease with increasing solvent polarity [710]. Analogously, the rate of solvolysis of triethyloxonium salts in ethanol/water mixtures decreases with increasing water content [490]. Solvolysis rates of A-t-alkylpyridinium salts such as 1-(1-methyl-l-phenylethyl)pyridinium perchlorate are almost independent of solvent polarity, whereas A-s ec-alkylpyridinium salts exhibit small decreases in rate with increasing solvent polarity [710]. The non-creation of charge in the activation process of these type (b) reactions much reduces the influence of solvent polarity on rate cf. Table 5-4. 

This was absent in the living equilibrated system and only a triplet at 8 = 1.17 was found (together with a triplet from the liberated diethyl ether centered at 6 = 1.14 ppm) X The chemical shift of the protons of the ethyl group located on the oxonium ion in the macro-ring should be close to that in the triethyloxonium salt. The absence of absorption in this region in the equilibrated system indicates that the growing species are predominantly linear. 

The proportions of oxonium and carbenium ions in the chain growth, as well as their relative reactivities, may markedly depend on the polymerization coixlitions and vary with monomer structure. The high values of rate constants of the reaction between carbenium cations and ethers or acetals make questionable Okada s interpretation of the 1,3-dioxane-triethyloxonium salts system It is impossible to observe, at room temperature, the individual ROCHl species with excess of such nucleophiles as diethyl ether. We would rather suggest that the signal at 11—13 ppm 6 ( H-NMR) or 175—180 ppm 6( C-NMR) is due to some exchanging protonated species. 

Actually, Seagusa ) studied the reversible alkylation of THF by triethyloxonium salt and obtained in CH2Q2 at 35 °C kj, = 4.2 10 mole 1 s l. This value is not very far from that estimated Enikolopyan a.o. 

Chemoselective (V-ethylation of Boc-amino acids can be accomplished without racemization via the corresponding dianions. Thus, (V-t-butoxycarbonylamino acid (35) was converted into dianion (36) by treatment with 2 equiv. of Bu Li, followed by the reaction with 1 equiv. of triethyloxonium tetrafluoro-borate to give (V-ethyl derivative (37) along with a trace of ethyl ester (38). On treatment with 2.2 equiv. of the triethyloxonium salt (36 R = Ph) gave (38 R = Ph) in 95% yield (Scheme 17). ... 

Alkylation of 1,2,4-triazine 1-oxides with triethyloxonium salts affords 4-alkyl-l-oxido-l,2,4-triazinium salts 9261 while alkylation of the 2-oxide with triethyloxonium salts yields the O-alkylated product 10.261 Reaction of 1,2,4-triazine 4-oxides with triethyloxonium salts produces 1-alkylated 1,2,4-triazinium salts 11.261... 

N-Alkoxy Pyridinium Salts /V-Alkoxy Pyridinium salts are obtained with relatively high yields by a reaction of pyridine /V-oxides with a triethyloxonium salt in methylene chloride or chloroform [13]. Quinolinium salts can also be prepared from the corresponding /V-oxides [40], In both cases, an anion exchange is not necessary since the triethyl oxonium salt is available with nonnucleophilic counter anions. The most frequently used photoinitiators of this type are shown in Chart 11.8. The spectral response of these salts is in 260-310 nm range [13],... 

Reaction of 6-methyl-3-trimethylsilyloxy-1,2,4-triazine 1-oxide (100) with alkylating agents gives, after aqueous work-up, 4-alkyl-6-methyl-l,2,4-triazin-3-one 1-oxides (101) (Equation (5)) <86JHC1613>. Alkylation of the 1,2,4-triazine 1-oxides (102a-c) with triethyloxonium salts yielded 4-alkyl-l-oxy-l,2,4-triazinium salts (103a-c) (Equation (6)) <95UP6il-oi>. 

Propylaziridine, 1-isobutylaziridine, 1-phenylaziridine and l-(2-hydroxyethyl)-aziridine do not form cyclic oligomers in CH2C12 solvent with triethyloxonium salt initiator4 . 

Oxygen.—A kinetic study of the decomposition of triethyloxonium salts, [OEtalA ([A] =[BF4] , [PFe]", or [SbFg]-) in methylene chloride has been studied. The decomposition is strongly affected by the presence of EtOEt or dioxan. The mechanism is suggested to involve a four-centre transition state. ... 

Decontamination of laboratory wastes using triethyloxonium salts ... 

Oxonium, carbenium, or oxocarbenium salts generate tertiary oxonium ions in single step, as shown in Scheme 8 for initiation with triethyloxonium salt. 

Although a wide variety of substituted N-alkoxypyridinium salts have been prepared and evaluated as cationic photoinitiators, the simplest and most useful alkoxypyridinium salt is N-ethoxypyridinium hexafluoridophosphate, 99. This photoinitiator is prepared by the reaction of pyridine-N-oxide with a triethyloxonium salt bearing a non-nucleophilic anion such as PFg" as depicted in eqn [61]. The preparations of photoinitiators 100-103 shown earlier were carried out in a similar manner. 

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