Amination of alcohols

A thorough investigation has shown that the Tanigawa amination of alcohols, in which the corresponding alkoxide (282) is treated in DMF with A-methyl-A-phenylamino-triphenylphosphonium iodide (283) and a secondary amine at 80 °C, does not proceed at this temperature. In situ generation of the A.A-dimethylamino analogue (284) by reaction of (283) with dimethylamine, however, does lead to a smooth reaction at 90 °C. The proposed mechanism involves a pentacoordinated intermediate (285). " ... 

Another means of producing Michael acceptors is by the oxidation of unsaturated amines of alcohols, such as allyl amine (equation 9.16). 

Lower aliphatic amines are widely used as intermediates for the synthesis of herbicides, insecticides and drugs or can be applied as rubber accelerators, corrosion inhibitors, surface active agents etc. [l]. The most widespread method for the preparation of lower aliphatic amines involves the reaction of ammonia with an alcohol or a carbonyl compound in the presence of hydrogen. The most common catalysts used for reductive amination of alcohols, aldehydes and ketones contain nickel, platinum, palladium or copper as active component [ I — 3 ]. One of the most important issues in the reductive amination is the selectivity control as the product distribution, i.e. the ratio of primary to secondary or tertiary amines, is strongly affected by thermodynamics. 

Copper-catalysts promoted with i) other group VIA or VIIIA metals and ii) alcaline or alcaline earth elements (IA or IIA) are used for selective hydrogenation of various organic compounds (1). Moreover Cu(Co) Zn-Al catalysts were extensively studied for the synthesis of methanol and of light alcohols (2,3). More recently, due to the development of fine chemical processes, detailed studies of copper catalysts were carried out in order to show, like for noble metals, the effect of supports (SMSI), of promoters and of activation-on metal dispersion or reduction, on alloy formation... For example modified copper catalysts are known for their utilization in the dehydrogenation of esters (4-6), in the hydrolysis of nitriles (7), in the selective hydrogenation of nitriles (8), in the amination of alcohols (9)... 

Now the influence of water or ammonia on copper catalysts is being investigated. Previously A. BAIKER and coll, have shown that ammonia could modify the catalytic properties of copper catalysts used in the amination of alcohols (9). These authors noticed the formation of copper nitride after NH3 exposure at a temperature of about 300°C which is the reaction temperature of our study. The first results that we obtained in our study showed that both H2O and NH3 decrease significantly the copper dispersion in unpromoted catalysts and that this modification is less significant when Ca or Mn are added to the Cu-Cr catalyst. We are now studying what are the superfical modifications consecutive to the addition of promoters or/and water and ammonia. 

Besides oxidation reactions, MTO supported on AI2O3/ Si02, niobia, or zeolites also catalyzes the metathesis of functionalized alkenes, 1,2 transposition of allylic alcohols, addition of epoxides to ketones, alkoxylation of epoxides, dehydration and amination of alcohols, and... 

MTO has also been claimed to be the first transition metal complex to catalyze the direct, solvent-independent formation of ethers from alcohols [30]. Aromatic alcohols give better yields than aliphatic ones and reactions between different alcohols have been used to prepare asymmetric ethers. Also catalyzed by 1 is the dehydration of alcohols to form olefins at room temperature. When primary or secondary amines, respectively, are used as the limiting reagents, direct amination of alcohols gives the expected secondary or tertiary amines in yields of ca. 95 %. Disproportionation of alcohols to carbonyl compounds and alkanes is also observed for aromatic alcohols in the presence of MTO as catalyst. 

The amination of alcohols and carbonyl containing compounds in the presence of a molten iron catalyst ... 

In order to corroborate the main steps of the synthesis of dimethylethylamine and of the main by-products, we studied the reactivity of some intermediates and products with or without reagents (MEA, MeOH) under the same experimental conditions i) In the absence of methanol (replaced by n-heptane), monoethylamine is transformed mainly into diethylamine (DEA), the deactivation of the catalyst being very fast due to an increase of the formation of ammonia (15). Baiker and Kijenski showed, for instance, that part of the copper was transformed into copper nitride during the amination of alcohols (12). In the presence of methanol, the monoethylamine surface coverage is lower and a decrease cf the DEA formation can be observed. Methanol acts as an inhibitor in the synthesis of DEA and as a promotor of the catalyst duration. 

This chapter focuses on the metal-catalyzed amination of alcohols and related compounds such as aminoalcohols, phenols and di- and polyhydroxy compounds. Details of the synthesis of amines with acidic catalysts, including zeolites, mixed oxides and metal phosphates, can be found elsewhere [3,5-7]. 

All metal hydrogenation catalysts including supported Pt metals, Cu, Co, Ni, Fe, and Cu-Cr203 are suitable for amination of alcohols [2,11]. There is a wide range of commercially available metal amination catalysts and development of a special multicomponent catalyst might be necessary for demanding reactions only [9]. The choice of a particular catalyst is determined mainly by its selectivity pattern... 

The amination reaction, forming primary, secondary, and tertiary amines, can be between alcohols, aldehydes, or ketones, and ammonia and hydrogen. Sabatier and Mailhe in 1909 [1] first reported the synthesis of amines from alcohols. Over the course of the 20 century the in jortance of these compounds has increased and amines are key intermediates and final products within the fine chemical, agrochemical, and pharmaceutical industries. The amination of alcohols to form amines has been the subject of a number of mechanistic studies [2-8] proposing a variety of mechanisms. In this study we have investigated the... 

The Reductive Amination of Alcohols with Foraminate Catalysts. The remarkably good results which can be obtained with the foraminate-catalyst system in this type of reaction can be easily demonstrated by the following experimental results obtained in the reductive amination of three butanols over a baryta-treated nickel-aluminum foraminate catalyst operating at 190 C, 250 psi, and a liquid-alcohol space velocity of 0.2 hr. Ih this series of experiments an alcohol ammonia hydrogen mole ratio of V. 1.25 2.5 was used. From these results certain general features of the re-... 

Some examples of bubble fixed-bed reactors apphcation are the hydrogenation of nitro compounds, amination of alcohols, and ethylnylation of formaldehyde to butynediol (Raniachandian and Chaudliari, 1984). 

Having established the importance of the calculated parameters in the studies of physical data we turned our attention to the problem of chemical reactivity. It could be shown that the values for the inductive and polarisability effect can be used to calculate reactivity data of some fundamental polar reactions in the gas phase (Figure 6). Linear equations could be developed to calculate proton affinities of amines/ of alcohols and ethers/ and of thiols and thioethers/ as well as gas phase acidity data of alcohols. ... 

It is the amination of alcohols to methylamines according to equation 2, which are of considerable technical importance. Using conventional acid heterogeneous catalysts like alumina one obtains a product mixture at around 325 °C which is almost equivalent to the equilibrium composition. 

SCH EME 4.25 The water-soluble calix[4]resorcinols as catalysts in the amination of alcohols. 

Shirakawa S, Shimizu S. Dehydrative amination of alcohols in water using a water-soluble calix[4]resordnarene sulfonic acid. Synlett 2008 10 1539-42. 

Scheme 21 [Cp IrCl2]2-catalyzed amination of alcohols with ammonium salts, carbamates, amides, sulfonamides and primary heteroarylamines...

Some iV-alkylation reactions catalyzed by other noble metal catalysts have also been reported. In 2011, Gusev and co-workers reported an Osmium complex-catalyzed N-alkylation of amines at 200 °C with a low catalyst loading (0.1 mol%) [122]. In 2014, Zhu and co-workers disclosed a [ReH7(PCy3)2]-catalyzed amination of alcohols with anilines under CO atmosphere (Eq. 29) [123]. The authors proposed that coordination of CO with Re might lead to decomposition of ReH7(PCy3)2 to a rhenium carbonyl complex, which was believed to be the active... 

In 2013, Shimizu and co-workers first reported an additive-free Ni/Al203-catalyzed synthesis of primary amines from alcohols and ammonia (Scheme 27) [154]. The recovered catalyst could be reused at least twice without losing catalytic activity (1st, 88 %, 3rd, 89 %). Later in 2013, the authors extended the method to amination of alcohols with anilines and aliphatic amines (Scheme 27) [155]. In 2014, the Shimizu group also described a Ni/CaSi03-catalyzed amination reaction of alcohols with ammonia, anilines and aliphatic amines [156]. 

Scheme 27 Ni/AhOs-catalyzed amination of alcohols with ammonia, aniUnes, and aliphatic amines...

Later in 2012, Corma, Sabater and co-workers reported a nano-Au/CeOa-catalyzed IV-alkylation of amines with alcohols [167]. In 2014, De Vos and coworkers reported a nano-Ag/Al203/Ga203-catalyzed amination of alcohols with a variety of aliphatic and aryl amines under mild conditions [168]. The catalyst remained active for at least three runs (1st, TOP = 1.01/h 3rd, 1.02/h). 

Scheme 30 Tentative mechanism for amination of alcohols catalyzed by carbon material 21...

In 2014, by employing the hydrogen autotransfer method, Zhao and co-workers reported the first enantioselective amination of alcohols to chiral secondary arylamines in high yields and high ee up to 97 % (Eq. 56, Scheme 31) [178]. Intramolecular amination could also be achieved to give quinoline 24 with 68 % ee. The authors proposed that the high enantioselectivity might be attributed to the cooperation of the iridium complex 25 and the chiral phosphoric acid 26. 

Scheme 32 Proposed mechanism for the dynamic Mnetic asymmetric amination of alcohols...

In 2015, Zhao and co-workers described the first dynamic kinetic asymmetric amination of alcohols via borrowing hydrogen methodology under the cooperative catalysis of iridium complex 25 and chiral phosphoric acid 27 (Schemes 31, 32) [179]. The authors proposed that, initially, the two stereocenters in the alcohols were both racemized to ketone by the first oxidation, followed by tautomerization of the iminium intermediates 28 and 30 through enamine intermediate 29. Then, the... 

Tillack A, Hollmann D, Beller M et al (2008) Salt-free synthesis of tertiary amines by ruthenium-catalyzed amination of alcohols. Eur J Org Chem 28 4745-4750... 

Imm S, Bahn S, Beller M et al (2011) Improved ruthenium-catalyzed amination of alcohols with ammonia synthesis of diamines and amino esters. Angew Chem Int Ed 50(33) 7599-7603... 

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