Mechanistic Studies into Metal‐Catalyzed Aldoxime to Amide Rearrangements

The metal‐catalyzed rearrangement of aldoximes into primary amides is a completely atom economical synthetic method for the preparation of one of the most important functional groups in chemistry. There have been several reports of various metals successfully catalyzing this reaction, however, there are conflicting views as to the mechanism involved. Herein we report new experimental evidence to support the mechanism and whether this is universal to all catalysts reported or metal specific. We also describe our further studies into the mechanism of the nickel‐catalyzed acylation of amines with aldoximes.     

The temperature's influence on the selectivity between HNCO and HCN from pyrolysis of 2,5-diketopiperazine and 2-pyridone

Two cyclic amides, 2-pyridone and 2,5-diketopiperazine (DKP), were pyrolysed at temperatures ranging from 700 to 1100 °C. Pyridone is the only one of the four main nitrogen functionalities found in coal that is likely to form HNCO under pyrolysis. DKP is a primary pyrolysis product from proteins, which are the main nitrogen source in biomass. The formation of HNCO from biomass has been suggested to originate from DKP and other cyclic amides. The aromatic 2-pyridone was thermally more stable than the non-aromatic DKP. Both amides formed HCN, HNCO and NH₃. The NH₃ yields, about 3-4% for 2-pyridone and 10% for DKP, were almost independent of temperature. The HCN yield on the other hand showed strong temperature dependence and increased with temperature for both of the cyclic amides. The HNCO yield decreased with increasing temperature for DKP over the whole temperature interval. For 2-pyridone, the pyrolysis was incomplete at the lowest temperature in the investigation. Between 900 and 1100 °C, the pyrolysis of 2-pyridone was complete and the HNCO yield decreased with increasing temperature. The HNCO/HCN ratio for both of the cyclic amides decreased with increasing temperature over the whole investigated temperature range. The finding in literature that the HNCO formation from cracking of coal tars produced a maximum HNCO yield at an intermediate temperature, is explained by the thermal stability of pyridone at low temperatures and the selectivity towards HCN at high temperatures.     

Biocatalytic Synthesis of Nitriles through Dehydration of Aldoximes: The Substrate Scope of Aldoxime Dehydratases

Nitriles, which are mostly needed and produced by the chemical industry, play a major role in various industry segments, ranging from high‐volume, low‐price sectors, such as polymers, to low‐volume, high‐price sectors, such as chiral pharma drugs. A common industrial technology for nitrile production is ammoxidation as a gas‐phase reaction at high temperature. Further popular approaches are substitution or addition reactions with hydrogen cyanide or derivatives thereof. A major drawback, however, is the very high toxicity of cyanide. Recently, as a synthetic alternative, a novel enzymatic approach towards nitriles has been developed with aldoxime dehydratases, which are capable of converting an aldoxime in one step through dehydration into nitriles. Because the aldoxime substrates are easily accessible, this route is of high interest for synthetic purposes. However, whenever a novel method is developed for organic synthesis, it raises the question of substrate scope as one of the key criteria for application as a “synthetic platform technology”. Thus, the scope of this review is to give an overview of the current state of the substrate scope of this enzymatic method for synthesizing nitriles with aldoxime dehydratases. As a recently emerging enzyme class, a range of substrates has already been studied so far, comprising nonchiral and chiral aldoximes. This enzyme class of aldoxime dehydratases shows a broad substrate tolerance and accepts aliphatic and aromatic aldoximes, as well as arylaliphatic aldoximes. Furthermore, aldoximes with a stereogenic center are also recognized and high enantioselectivities are found for 2‐arylpropylaldoximes, in particular. It is further noteworthy that the enantiopreference depends on the E and Z isomers. Thus, opposite enantiomers are accessible from the same racemic aldehyde and the same enzyme.     

Castor-based derivatives: Synthesis of some amides

Various amides of ricinoleic acid and the related ricinelaidic, hydroxystearic, dihydroxystearic, and trihydroxystearic acids have been synthesized and characterized. Ester aminolysis in methanol solution with sodium methoxide catalyst at room temperature has limited utility since it suffers severe rate retadations due to steric effects with secondary amines. In addition, with primary amines and ammonia, extended reaction times are generally necessary for reasonable, yields. The use of mixed carboxylic-carbonic anhydrides in amide syntheses was investigated and found applicable without interference from the secondary hydroxyl groups. Also, no appreciable steric effects were observed with most amines. This rapid, high yield method has been employed in the synthesis of a number of new amides from castor-based acids, ammonia, and primary and secondary amines. Presented at the AOCS meeting, New Orleans, La., 1962. A laboratory of the Western Utiliz. Res. & Dev. Div., ARS, U.S.D.A.     

Continuous deacylation of amides in a high-temperature and high-pressure microreactor

The deacylation of amides, which is widely employed in the pharmaceutical industry, is not a fast reaction under normal conditions. To intensify this reaction, a high-temperature and high-pressure continuous microreaction technology was developed, whose space-time yield was 49.4 times that of traditional batch reactions. Using the deacylation of acetanilide as a model reaction, the effects of the temperature, pressure, reaction time, molar ratio of reactants, and water composition on acetanilide conversion were carefully studied. Based on the rapid heating and cooling capabilities, the kinetics of acetanilide deacylation at high temperatures were investigated to determine the orders of reactants and activation energy. This microreaction technology was further applied to a variety of other amides to understand the influence of substituents and steric hindrance on the deacylation reaction.     

The electrochemistry of nitrate-amide melts: Reactions of nickel and copper in nitrate-amide melts

Copper and nickel may be electrodeposited from their ions in solution in nitrate-amide melts at room temperature. In the ammonium nitrate-acetamide-urea melt at 23°C, the reduction to the metal competes with the corrosion reaction at low rates and with the reduction of the ammonium and nitrate ions of the melt at high current densities. Two distinct types of nickel complexes are found in solution. The nickel complex formed by the corrosion reaction is bound by at least one ammonia ligand. Nickel complexes formed by dissolving the halide in the melt show evidence of coordination by less strongly bounding ligands, probably by amides. Similarly, the visible spectra of copper chloride in solution suggest that the cupric ions are coordinated primarily by amides. The copper corrosion reaction produces a complex with a spectra distinctly different from that of cupric chloride in solution. The shift in absorption maxima suggests that the copper complex formed by the corrosion reaction has at least one ammonia ligand in the coordination sphere.     

A novel technique for the preparation of secondary fatty amides

A technique for the synthesis of monosubstituted fatty amides at low temperature and ambient pressure was developed. This method involved the condensation of an amine with a triacylglycerol. The primary amine (ethyl,n-butyl,n-hexyl andn-octyl were tested) acted as reagent and solvent for the fatty substrates. No additional organic solvent or catalyst was added. Tallow, vegetable oils and fish oil all served well as substrates, as did pure tripalmitin. The rate of amidation was dependent upon temperature and the ratio of fat to amine. In a series of experiments conducted with tallow andn-butylamine at a fat:amine molar ratio of 1:16, amidation could be carried out at 20°C, producingn-butyltallowamide in 83% yield in 24 hr. When the fat:amine molar ratio was reduced to 1:8, and the temperature raised to 45°C, the amide yield was 87.6% in 24 hr. When the reaction was carried out at the boiling point ofn-butylamine (78°C) and at a fat:amine ratio of 1:8, the amide yield was 93.2% in 4 hr. The reaction progressed more rapidly with higher molecular weight amines. The identity and purity of the amides was assessed by thin-layer chromatography and confirmed by elemental analyses and infrared and C¹³ nuclear magnetic resonance spectroscopy.     

Biocatalytic production of 10-hydroxystearic acid, 10-ketostearic acid, and their primary fatty amides

The objective of this study was to develop scaleup bioprocesses for producing 10-hydroxystearic acid (10-HSA) and 10-ketostearic acid (10-KSA) as well as their primary amides for potential new uses. A reactor process was examined to obtain the mono-oxygenated FA using Sphingobacterium thalpophilum (NRRL B-14797) and Bacillus sphaericus (NRRL NRS-732), which solely produce 10-HSA and 10-KSA, respectively, from technical-grade oleic acid. By using an 8-h-old B-14797 culture grown in a manganese-containing WF6 medium, pH 7.3, at 28°C under 350 rpm agitation and 0–50% dissolved oxygen concentrations provided by a controlled sparger aeration, the production of 10-HSA reached 7 g/L with a 40% yield in 4 d. In using a 12-h-old NRS-732 culture grown in a pyruvate-containing PF6 medium, pH 6.5, at 30°C under 750 rpm agitation without any sparger aeration during the conversion reaction, 10-KSA production reached 7.9 g/L with a yield of more than 54% in 72 h. The scaleup reactor process provided crystalline 10-HSA and 10-KSA for producting new primary amides via a lipase-catalyzed amidation reaction with yields of 94 and 92%, respectively. The primary amides of 10-HSA and 10-KSA displayed m.p of 115 and 120°C, respectively.     

Michael addition polymers from bisacetoacetates

Summary The Michael reaction was used to synthesize polymers from bisacetoacetyl esters and amides and a diacrylate. The reaction occurred readily at room temperature yielding semi-solid polymers with broad molecular weight distributions which narrowed as the reaction progressed. The polymers based on the amide had lower molecular weights than those based on the ester.     

SOLVENT EXTRACTION OP COPPER (II), NICKEL (II) AND COBALT(II) PROM HALIDE AND THIOCYANATE SOLUTIONS BY ALDOXIMES

The extraction of divalent copper, nickel and cobalt from acidic chloride solutions with solutions of heptaloxime, nonaloxime and 2-methyldekaloxime in toluene has been studied at 18*C.

These metals were found to be extracted according to the following solvation reaction:

The influence of syn-anti isomerization of aldoximes on the extraction has been discussed. Taking into account association and syn - anti isomerization constants of aldoximes in organic phase,hydration of extracted oomplexes and activities of salts in aqueous phase, effective extraction oonstants have been calculated for chloride solutions.

Separation of nickel and cobalt from aoidic chloride, bromide and thiooyanate solutions by extraction with heptaloxime has been studied.     

Solvent-free selective oximation of aldehydes using facile and reusable heterogenous polyoxometalate

The efficiency of various heteropoly compounds as well-known solid acids was investigated and a new procedure was developed for synthesis of Z-isomers of aldoximes. This method consistently has the advantage of excellent yields and short reaction times. Furthermore, the catalyst could be easily recovered after completion of the reaction and reused without a considerable loss of its activity.     

Dehydration of aldoximes on rare earth exchanged (La<Superscript>3+</Superscript>, Ce<Superscript>3+</Superscript>, RE<Superscript>3+</Superscript>, Sm<Superscript>3+</Superscript>) Na–Y zeolites: A facile route for the synthesis of nitriles

Rare earth exchanged Na–Y zeolites, H-mordenite, K-10 montmorillonite clay and amorphous silica-alumina were effectively employed for the continuous synthesis of nitriles. Dehydration of benzaldoxime and 4-methoxybenzaldoxime were carried out on these catalysts at 473 K. Benzonitrile (dehydration product) was obtained in near quantitative yield with benzaldoxime whereas; 4-methoxybenzaldoxime produces both Beckmann rearrangement (4-methoxyphenylformamide) as well as dehydration products (4-methoxy benzonitrile) in quantitative yields. The production of benzonitrile was near quantitative under heterogeneous reaction conditions. The optimal protocol allows nitriles to be synthesized in good yields through the dehydration of aldoximes. Time on stream (TOS) studies show decline in the activity of the catalysts due to neutralization of acid sites by the basic reactant and product molecules and water formed during the dehydration of aldoximes.     

Synthesis and isolation of epoxy secondary amidesvia direct amidation ofVernonia galamensis seed oil

Vernonia galamensis oil, containing naturally epoxidized triglycerides, was reacted withn-butylamine,n-pentylamine andn-hexylamine to afford high yields of epoxidized secondary amides. Three reaction conditions were investigated: (i) reflux with amines as solvents, (ii) reflux with hexane as the solvent and (iii) room temperature with the amines as solvents. Reactions with amines as refluxing solvents were completed in 1–5 h, while those with hexane went to completion within 2 to 5 d. Room temperature reactions were onlyca. 80% complete after several days. Reactivity was increased with higher amine homologs at both reflux and room temperature reaction conditions. Isolated yields of epoxy-containing amides were about 80% with purity exceeding 96% in all cases. Spectroscopic characterization of the previously unreported alkyl-vernolamides is provided.     

Nitrogen derivatives (Amides,diamides, nitriles,primary amines and oxides)

Without a doubt the nitrogen derivatives are the most broadly diversified family of fatty acid derivatives. Today they account collectively for perhaps 400 million pounds of products per year in the USA alone. Although fatty amides may be produced by a large number of synthetic routes, industrially only two are of any commercial importance. Diamides are the difunctional analogs of simple amides, and a typical one that is in medium scale production volume is ethylene bis(stearamide). Industrially, the production of fatty nitriles in the fatty acid derivative industry is exclusively by ammonolysis of fatty acids at temperatures somewhat above those required to produce amides, or roughly, 300–320 C. Both vapor phase catalytic and liquid phase ammonolysis processes may be employed. Nitriles have limited uses as such, but find their utility as fatty derivative intermediates only. The primary amines, RNH₂, are produced industrially by the catalytic hydrogenation of nitriles. The general conditions for the conversion of nitriles to primary amines with a minimum content of secondary or tertiary amines is with nickel catalyst using an excess of ammonia at relatively low temperatures (130–140 C). Amine oxides are derived from tertiary amines by a controlled reaction with hydrogen peroxide. In addition to tertiary amines, the monoalkyl diethoxylated amines can be considered as in the same class. These are made by the addition of ethylene oxide to primary amine. Two moles of ethylene oxide can be added without catalyst. Additional ethoxylation does require a basic catalyst. These amines, besides having end uses of their own, can be converted to amine oxides or can be converted to ethoxylated quaternary ammonium salts.     

Gallium (III) triflate catalyzed dehydration of aldoximes

Gallium triflate catalyzed dehydration of aldoximes to nitriles is described in good to excellent yields. Good catalytic and dehydrating capabilities of gallium triflate are demonstrated through this dehydration reaction.     

Hydration of 3-cyanopyridine to nicotinamide over MnO2 catalyst

A simple and an eco-friendly process for the hydration of 3-cyanopyridine to nicotinamide in the presence of manganese dioxide catalyst has been described. The reaction is conducted at moderate temperature with the reaction times of 5–8 h using an aqueous solution of 3-cyanopyridine. The effect of various reaction parameters on the yield of nicotinamide was studied. In most instances, nearly quantitative yields of amides are obtained without any by-products. The IR and ESCA findings of the catalysts are correlated with the catalytic activity.     

Lipase catalyzed formation of fatty amides

Certain lipase preparations were found to facilitate the preparation of fatty amides at 20°C in hexane. Lipase preparations investigated were from the fungiCandida rugosa, Rhizomucor miehei and porcine pancreas. Reactants were various primary alkylamines and fatty acid methyl esters or triglycerides. Moderate yields of fatty amides were obtained using aR. miehei lipase preparation which is immobilized on a solid support as catalyst, although all three lipase preparations showed some catalytic activity under these conditions and, in addition, showed different kinds of selectivity for fatty acid and alkylamine chain lengths. No reaction was observed in similar experiments using one fatty acid as the substrate or one secondary amine.     

The Determination of Fatty Acid Primary Amides by Capillary Gas Chromatography

A method has been developed for the determination of 12 primary amides of long-chain fatty acids by capillary column gas chromatography. The method uses no derivatization or sample preparation other than extraction of the sample. A variety of commercial amidecontaining materials have been analyzed successfully. The amides, along with other soluble materials, are first separated from the host using refluxing 2-propanol containing an internal standard. The fatty acid amides are then identified and measured by gas chromatography over a programmed temperature range of 200 to 260 C. The chromatograms obtained show sharp peaks, unique retention times and acceptable reproducibility for quantitation.Cis- trans isomers of several of the fatty acid amides were tested and found to be resolved under the conditions employed.     

Copper-Catalyzed Dehydration of Primary Amides to Nitriles

Abstract  

In the present study we introduce a copper-catalyzed protocol for the dehydration of primary amides to their corresponding nitriles applying N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) as silylation reagent. For that purpose investigations of various reaction parameters (copper source, solvent, temperature, MSTFA and copper loading) have been carried out to find suitable reaction conditions. Simple copper(I) chloride (2.5 mol%) and MSTFA (2.0 equiv) in toluene allow for the straightforward synthesis of a variety of nitriles (15 examples).     

Rational Biocatalyst Design for a Cyanide-Free Synthesis of Long-Chain Fatty Nitriles from Their Aldoximes

Recently, the capability of the aldoxime dehydratase from Bacillus sp. (OxdB) for the transformation of fatty aldoximes into fatty nitriles with impressive substrate loadings is reported. However, the substrate scope of this biocatalyst turned out to be limited in terms of the chain length with decanal oxime being the substrate with the longest well tolerated n-alkyl chain. Besides the increased bulkiness of the long-chain aldoximes, their strongly decreased water solubility represents a further hurdle for an efficient biotransformation. Addressing this challenge of an expanded substrate spectrum comprising long-chain fatty aldoximes, this work investigates the substrate solubility and enzyme kinetics in combination with molecular modeling in order to find an enzyme mutant being suitable for C12- to C16-aldoximes. Both, fatty aldoxime solubility in water and the active site of the wild-type enzyme OxdB are identified as critical issues for an efficient biotransformation of these substrates. The activity issue is addressed by a rational design of a mutant using a homology modeling as well as a molecular modeling software suitable for enzymes. With the resulting double mutant OxdB-F289A/L293A, this report can achieve successful biotransformations with the C12- to C16-aldoximes at substrate concentrations of 250 × 10⁻³ to 1000 × 10⁻³ m . For example, an excellent conversion of >99% is obtained with tetradecanal oxime. Practical applications: Fatty nitriles with a prolonged chain length of C12 or more are of high interest in industry due to their use for the production of fatty amines on large technical scale. As an alternative route, fatty nitriles can be generated from their aldoximes by means of an aldoxime dehydratase (Oxd) as biocatalyst. The conversion of long-chain fatty aldoximes, however, remained a challenge up to now. This work describes the optimization of the aldoxime dehydratase OxdB from Bacillus sp. for the dehydration of nonsoluble bulky fatty aldoximes. The created variant can convert long chain fatty aldoximes toward the corresponding nitrile as demonstrated for C12- to C16-nitriles. In addition, high conversion (of up to >99%) is achieved when operating at high substrate concentrations of up to 1000 × 10⁻³ m , thus making this approach interesting for industrial applications.