Hydrogenation autocatalytic

Formaldehyde condenses with itself in an aldol-type reaction to yield lower hydroxy aldehydes, hydroxy ketones, and other hydroxy compounds the reaction is autocatalytic and is favored by alkaline conditions. Condensation with various compounds gives methylol (—CH2OH) and methylene (=CH2) derivatives. The former are usually produced under alkaline or neutral conditions, the latter under acidic conditions or in the vapor phase. In the presence of alkahes, aldehydes and ketones containing a-hydrogen atoms undergo aldol reactions with formaldehyde to form mono- and polymethylol derivatives. Acetaldehyde and 4 moles of formaldehyde give pentaerythritol (PE) ... 

Electroless reactions must be autocatalytic. Some metals are autocatalytic, such as iron, in electroless nickel. The initial deposition site on other surfaces serves as a catalyst, usually palladium on noncatalytic metals or a palladium—tin mixture on dielectrics, which is a good hydrogenation catalyst (20,21). The catalyst is quickly covered by a monolayer of electroless metal film which as a fresh, continuously renewed clean metal surface continues to function as a dehydrogenation catalyst. Silver is a borderline material, being so weakly catalytic that only very thin films form unless the surface is repeatedly cataly2ed newly developed baths are truly autocatalytic (22). In contrast, electroless copper is relatively easy to maintain in an active state commercial film thicknesses vary from <0.25 to 35 p.m or more. 

There are many reactions in which the products formed often act as catalysts for the reaction. The reaction rate accelerates as the reaction continues, and this process is referred to as autocatalysis. The reaction rate is proportional to a product concentration raised to a positive exponent for an autocatalytic reaction. Examples of this type of reaction are the hydrolysis of several esters. This is because the acids formed by the reaction give rise to hydrogen ions that act as catalysts for subsequent reactions. The fermentation reaction that involves the action of a micro-organism on an organic feedstock is a significant autocatalytic reaction. 

The oxidation is autocatalytic, being catalyzed by the product, benzeneseleninic acid. If the temperature drops significantly below 30°, the addition of hydrogen peroxide should be stopped, and the ice-salt bath should be removed to maintain the rate of oxidation and avoid an accumulation of hydrogen peroxide in the flask. 

The oxidation of di-2-chloroethyl ether is first-order with respect to ether, but is autocatalytic and chloride ion is liberated. A hydrogen atom abstraction process, similar to that above, probably takes place, viz. 

According to Sanko and Stefanovskii the reaction between arsenic(III) and chlorate is autocatalytic in character and at constant hydrogen ion concentration the rate is given by... 

Similar results have recently been reported by Aspnes and Heller. They proposed an autocatalytic model for photoactive systems involving metal/compound semiconductor interfaces. To explain induction times in CdS systems (.9), they suggest that hydrogen incorporated in the solid lowers the barrier to charge transfer across the interface and thereby accelerates H2 production rates. 

A lactic acid/hydrogen fluoride/nitric acid mixture is used to polish metals. It is unstable and autocatalytic. After storing it for twelve hours the temperature rises to 90°C and there is significant gas release. Therefore such mixtures should not be kept. 

The interaction of hydrogen with preadsorbed oxygen at Pt(lll) led to hexagonal and honeycomb structures to develop at 131 K, which could be associated with OH phases with also evidence for water formation. The front (bright ring) consisted mainly of OH(a) and the area behind the front of H20(a). The mechanism suggested is that H(a) reacts first with 0(a) to form OH(a) and then H20(a) the water is mobile and reacts with O(a) to form OH(a) it is therefore an autocatalytic reaction. 

The autocatalytic reaction mechanism apparent at low temperatures is expected to apply to catalytic hydrogen oxidation at high pressures. In addition, the above study is the first to use STM to observe the formation of dynamic surface patterns at the mesoscopic level, which had previously been observed by other imaging techniques in surface reactions with nonlinear kinetics [57]. This study illustrates the ability of in situ STM to visualize reaction intermediates and to reveal the reaction pathway with atomic resolution. 

An autocatalytic reaction is one in which the reaction rate is proportional to a product concentration raised to a positive exponent. Some of the first articles in the literature of chemical kinetics deal with reactions of this type. For example, in 1857, Baeyer (12) reported that the reaction of bromine with lactose was autocatalytic. The hydrolyses of several esters also fit into the autocatalytic category, since the acids formed by reaction give rise to hydrogen ions that serve as catalysts for subsequent reaction. Among the most significant autocatalytic reactions are the fermentation reactions that involve the action of a microorganism on an organic feedstock. 

The pure peroxoacid, prepared at —80°C, decomposes explosively at —30°C. Solutions in acetic acid or water of below the limiting concentration (corresponding to a stoicheiometric mixture of 70% aqueous nitric acid and 100% hydrogen peroxide) are stable, while those above the limit decompose autocatalytically, eventually exploding [1], Explosion of the vapour when passed into a mass spectrometer inlet at 427°C (but not at 327°) was noted [2],... 

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