| 19% |
With 2-pyrazylcarboxylic acid; dipotassium peroxodisulfate; ferrocene; In water; acetonitrile; at 60℃; under 7600.51 Torr; for 4h;Autoclave; |
General procedure: The hydrocarboxylation experiments were performed following the previously developed protocol [31-35]. The reaction mixtures were placed into a 13.0-mL stainless steel autoclave, equipped with a Teflon-coated magnetic stirring bar. Then the autoclave was closed and flushed with CO three times for removing the air and finally pressurized with CO (CAUTION: due to the toxicity of CO, the heating oven should be located in a well-ventilated hood.) The reaction mixture was stirred using a magnetic stirrer and an oil bath, whereupon it was cooled in an ice bath, degassed, opened and the contents transferred to a flask. Diethyl ether and cycloheptanone (GC internal standard) were added. The obtained mixture was vigorously stirred for 10 min, and the organic layer was analyzed typically by GC [a Fisons Instruments GC 8000 series gas chromatograph equipped with30 m×0.22 mm×25 mum, BP20 (SGE) capillary column (helium was the carrier gas) |
| 29.6%Chromat. |
With dipotassium peroxodisulfate; water;[OCu4{N(CH2CH2O)3}4(BOH)4][BF4]2; In acetonitrile; at 50℃; under 16341.1 Torr; for 6h;Product distribution / selectivity; |
In a typical experiment the reaction mixtures were prepared as follows. To a 13.0 mL stainless steel autoclave, equipped with a Teflon-coated magnetic stirring bar, were added 0-32.0 mumol (typically 8.0 mumol) of catalyst (optional), 1.00-2.00 mmol (typically 1.50 mtnol) <n="10"/>of K2S2O8, 2.0-3.0 mL of H2O, 2.0-4.0 mL of MeCN and 1.00- 1.50 mmol (typically 1.00 mmol) of liquid alkane (in the case of pentane, cyclopentane, hexane and cyclohexane) . Then the autoclave was closed and flushed with dinitrogen three times for removing the air and pressurized with 20-40 atm (typically 20 atm) of carbon monoxide. In the case of using a gaseous alkane (ethane, propane or ?-butane) , the reactor had been pressurized with 1-10 atm of this gas prior to the admission of CO. The reaction mixture was vigorously stirred for 2-6 h at 25-60 0C using a magnetic stirrer and an oil bath, whereupon it was cooled in an ice bath, degassed, opened and transferred to a Schlenk tube. Diethyl ether (9.0-11.0 mL) , to separate from the inorganic compounds, and cycloheptanone (90 muL, internal standard) were added. The obtained mixture was vigorously stirred and the organic layer was analyzed by gas chromatography (internal standard method) using a Fisons Instruments GC 8000 series gas chromatograph with a DB WAX fused silica capillary column (P/N 123-7032) and the Jasco-Borwin v.1.50 software. In some cases, the products were also identified by GC-MS, 1H and 13C-(1Hj NMR techniques, using a Trio 2000Fisons spectrometer with a coupled Carlo Erba(Auto/HRGC/MS) gas chromatograph, and a Varian UNITY 300NMR spectrometer, respectively. The catalysts have been obtained either according to the previously described methods t3a'4a'12] or from commercial sources.Examples of effects on the alkane carboxylation of various factors, such as the relative amounts of alkane, <n="11"/>carbon monoxide, oxidant, solvent and its composition, catalyst type and reaction temperature, are listed in Tables 1 and 2 and discussed below.2 - Examples; The carboxylation of alkanes typically proceeds more efficiently in the presence of a metal catalyst, thus leading to higher yields of carboxylic acids which can usually be achieved in a shorter reaction time and at lower reaction temperature, in comparison with the same reaction performed in the absence of catalyst.The tetracopper triethanolaminate complex [OeCu4(N(CH2CH2O)3J4(BOH)4] [BF4] 2 exhibits the highest level of activity among the tested catalysts (Table 2) . For this catalyst, the maximum overall yields for the various alkanes are in the following order: cyclohexanecarboxylic acid from cyclohexane {ca. 72%, example 15) , 2- methylhexanoic and 2-ethylpentanoic acids from rz-hexane(ca. 45%, example 14), isobutyric and butyric acids from propane {ca. 38%, example 9), 2-methylbutanoic acid from n- butane [ca. 30%, example 10) , 2-meth.ylpentanoic and 2- ehtylbutanoic acids from n-pentane (ca.. 23%, example 11) , cyclopentanecarboxylic acid from cyclopentane (ca. 22%, example 12), and propionic acid from ethane (ca. 9%, example 8) . The yields based on the peroxodisulphate oxidant are also high, being typically h, of those based on alkane; Other catalysts, namely [Cu2 (H2tea) 2{ C5H4 (COO) 2- l,4}]n-2omegaH2O, [Cu(H2tea) (N3)] , Cu (NO3) 2 ? 2.5H2O,Ca[V(ON(CH2COO)2J2] , K2Cr2O7, MnO2 and Fe (OH) 3 ? 0.5H2O, can also be applied for the carboxylation of e.g. cyclohexane <n="14"/>leading to yields of cyclohexanecarboxylic acid in the 14-39% range (Table 2, examples 17-23) .The catalyst amount has only a slight effect on the product yield, but lower catalyst amounts lead to quite higher TONs. For example, in the case of cyclopentane carboxylation, a catalyst amount decrease from 8.0 to 2.0 mumol leads only to a slight yield lowering from 22.2 to20.5%, whereas the TON increases from 42 to 153 (Table 2, examples 12 and 13) .In both metal-free and metal-catalysed processes the secondary carbon atom in alkanes is more easily carboxylated favouring the formation of branched carboxylic acids. Moreover, the partial oxidation of linear alkanes to carboxylic acids (typically occurring in TFA containing systems) or to alcohols and ketones does not proceed, to a considerable extent, in our processes.The efficiency of both metal-free and metal- catalysed processes for alkane carboxylation is dependent on various factors, namely the amount and composition of solvent mixture (the 1:1 or 1:2 H2O/MeCN volumetric ratio usually is very favourable but not an exclusive one) , and the CO pressure (the highest yields and selectivities are commonly achieved for the typical CO pressure of 20 atm) . Nevertheless, other factors such as the type and amount of catalyst, oxidant amount, relative amounts of all the reaction components and reaction time, also influence the obtained results. |
Chemistry
Pharmaceutical Intermediates
Inhibitors/Agonists
Material Science
HazMat Fee +
For Research Only
110K+ Compounds
Competitive Price
1-2 Day Shipping
