Selective to aldehyde

Bromo-2-phenylsulfonyl-2-butene adds with syn selectivity to aldehydes indicating again that in the intermediate chromium species the 3-alkyl group is forced to occupy the position trims to the bulky 2-substituent20,21. 

Dioxygen is a cheap and ideal source of oxygen but it is very difficult to activate and there are relatively few examples of 02 oxidations catalyzed by zeolite-encapsulated complexes. Encapsulated CoPc is active for the oxidation of propene to aldehyde, whereas the free complex is inactive.104 A triple catalytic system, Pd(OAc)2, benzoquinone, and a metal macrocycle, was used to oxidize alkenes with molecular oxygen at room temperature.105 Zeolite-encapsulated FePc106-108 and CoSalophen (Scheme 7.5)107109 complexes were used as oxygen-activating catalysts. With the use of a Ru complex instead of Pd(OAc)2 in the triple catalytic system, primary alcohols can be oxidized selectively to aldehydes.110... 

The hydroformylation reactions were carried out in a number of different solvent systems, Table 2, at 50-60°C and 40 bar CO/H2 (1 1) using the (S,R)-1 m-C6F13(CH2)3]2-BINAPHOS ligand, Figure 6.11. After 18 hours in the PFMC/toluene system, 100% conversion was achieved with 100% selectivity to aldehydes of which 92% were... 

Olefin feed h3/co Linear isomer (%) Selectivity to aldehyde (%)... 

Alkylation of aldehydes.1 R(Pb in combination with 1 equiv. of TiCl4 adds selectively to aldehydes in CH2C12 at temperatures of - 78-0°. Yield of adducts is greater than 70% in the case of (QHs Pb or Bu4Pb. Ketones do not react with... 

The cationic rhodium catalysts with bisphosphine-modified CD-s were highly active in the biphasic hydroformylation of 1-octene (Scheme 10.8) [9,11]. In a two-phase system of l-octene/30 % DMF in water, quantitative conversion was obtained with 0.03 mol % of the catalyst at 80 °C and 100 bar syngas within 18 h (TOP = 180 h" ). Selectivity to aldehydes was higher than 99 % with 76 % regioselectivity in favour of the straight-chain product. 

Here we report on a new TEMPO based catalyst system for the oxidation of primary and secondary alcohols selectively to aldehydes and ketones using NaOCl as a terminal oxidant. 

Table 1. Oxidation of alcohol, 1 selectively to aldehyde 2 using KBr and Na2B40y based systems ...

Selectivity to aldehydes medium low high high high... 

The reagent in question is capable of reducing tertiary amides selectively to aldehydes. 

Synthetically, the question of which product is formed from a given carbonyl compound, the pinacol or the alcohol, is obviously of great interest. We have already noted the critical importance of the proton-donating ability of the medium in this respect. Attention has turned to the effect of other variables on the pinacol/alcohol ratio. Formaldehyde can be reduced cleanly to ethylene glycol at an electrode composed of a special type of carbon, in a process of potential commercial significance50. Nonaka and coworkers have found that reduction of aldehydes proceeds more selectively to aldehydes at nickel-Teflon-silica gel composite electrodes51. Nonaka and coworkers have also shown that for aromatic... 

These protocols can be regarded as promising because of their simplicity and broad scope. The conventional method for the production of aldehydes from alkenes consists of ozonolysis followed by workup under reducing conditions [72]. The ruthenium-based method, using either oxone or NaI04 as the oxidant, is an interesting alternative. The high selectivity to aldehyde versus carboxylic acid was reached by manipulation of the amount of terminal oxidant (2 Eq.) and the reaction time. 

Diisobutylaluminum hydride, formula ( -Bu)2A1H. Used to reduce nitriles and esters selectively to aldehydes, (p. 834)... 

Ligand Hex-l-ene % Isomerised hexenes % 2-ethyl- pentanal % 2-methyl- pentanal % Heptanal % Conversion % Selectivity to aldehydes % n i ratio... 

The move from a cobalt- to a rhodium-based process that was seen in methanol carbonylation (Section 4.2.4) is echoed in hydroformylation, thus the late 1960s saw the development of rhodium catalysts here too. Wilkinson and his colleagues found that RhH(CO)(PPh3)2 was an outstanding catalyst as it was very selective to aldehyde products (no alcohol formation, no alkene hydrogenation or isomerization occurred) and that very high n-ji- aldehyde selectivities of 20 1 for a... 

Alkenylchromium compounds. Addition of CrCh to a vinyl iodide or bromide in DMF forms a vinylchromium compound that adds selectively to aldehydes to form an ally lie alcohol. CrCl, also effects addition of iodobenzene to aldehydes to form benzyl alcohols. 

In 1952, it was discovered by Schiller that rhodium salts generated highly active hydroformylation catalysts. It was from these early studies that rhodium was estimated to be 1000 to 10 000 times more active than cobalt. Rhodium was also found to be very selective to aldehydes, with httle hydrogenation to alcohols observed under normal catalysis conditions. It was suggested early on that HRh(CO)4 was the active catalyst species, analogous to HCo(CO)4, and the same monometallic mechanism was proposed (Scheme 6). 

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