Double reaction

Particularly alkyl halides which have a perfluoroalkyl group at the /3-position undergo smooth carbonylation. Probably the coordination of fluorine to form a five-membered chelate ring accelerates the reaction. Double carbonylation to give the a-keto amide 915 is possible in Et NH with the fluorine-bearing alkyl iodide 914[769,770]. The ester 917 is obtained by the carbonylation of the /3-perfluoroalkyl iodide 916 in ethanol. 

Esters and acetylated hydroxyl groups are completely stable under the experimental conditions, but with ketals 10 29,110,112 yields are generally observed in the thermal reaction. Double bonds do not seem to interfere seriously with the course of the reaction provided that the geometric relationship of the free hydroxyl group to the angular methyl group is not changed drastically. In some cases allylic acetoxylation occurs, e.g., at C-7 of A -steroids. ° Ketones are usually stable (especially under photo-lytic conditions) but occasionally a-acetoxylation has been observed. 

Hazer [20,25] reported on the reaction of a po]y(eth-ylene g]ycol)-based azoester with methacryloyl chloride in the presence of (CH3CH2)3N. In this reaction double bonds were attached to the chain ends of the poly(ester) thus obtaining a macroinimer. Being used for the thermal polymerization of styrene, the material formed an insoluble gel [20]. Probably, both the C=C double bonds and the azo bonds reacted in the course of the thermal treatment. The macroninimer in a later work [25] was used for thermally polymerizing poly(butadiene) thus leading to poly(ethylene glycol-/ -butadiene) block copolymers. 

It is interesting to note the chemoselectivity of the reaction double and triple bonds, thioketals, epoxides, nitro and sulfone groups and usual functions are not affected. 

Rates of reaction usually go up when the temperature increases, although in catalysis this is only partly true as we will see later in this chapter. As a (crude ) rule of thumb, the rate of reaction doubles for every 10 K increase in temperature. 

When ionic compounds dissolve in water, the ions in the crystal separate and move throughout the solution. When two such solutions are mixed, all types of positive ions in the new solution are attracted to all types of negative ions in the solution. Sometimes a reaction takes place. This reaction is called a double-replacement reaction. Double-replacement reactions are sometimes called ionic reactions. 

Just as with replacement reactions, double-replacement reactions may or may not proceed. They need a driving force. The driving force in replacement reactions is reactivity here it is insolubility or covalence. In order for you to be able to predict if a double-replacement reaction will proceed, you must know some solubilities of ionic compounds. A short list of solubilities is given in Table 7-2. 

EXAMPLE 19.1. In a certain reaction, doubling the initial concentration of the only reactant doubles the initial rale of the reaction. What is the order of the reaction ... 

Scheme 6/1.50. Stille reaction/double-thermal-electrocyclization.

Typically, for a 10 K rise in temperature, the rate of a chemical reaction doubles. 

It is sometimes stated as a rule of thumb that the rate of a chemical reaction doubles for a 10 K increase in T. Is this in accordance with the Arrhenius equation Determine the... 

Scheme 1 Schematic representation of cycloaromatization reactions. Double lines correspond to the out-of-plane re-systems of a bis-alkyne reagent. Only orbitals of the in-plane re-system in the reactant and of new

This chapter has introduced the aldol and related allylation reactions of carbonyl compounds, the allylation of imine compounds, and Mannich-type reactions. Double asymmetric synthesis creates two chiral centers in one step and is regarded as one of the most efficient synthetic strategies in organic synthesis. The aldol and related reactions discussed in this chapter are very important reactions in organic synthesis because the reaction products constitute the backbone of many important antibiotics, anticancer drugs, and other bioactive molecules. Indeed, study of the aldol reaction is still actively pursued in order to improve reaction conditions, enhance stereoselectivity, and widen the scope of applicability of this type of reaction. 

Quantitative measurements of simple and enzyme-catalyzed reaction rates were under way by the 1850s. In that year Wilhelmy derived first order equations for acid-catalyzed hydrolysis of sucrose which he could follow by the inversion of rotation of plane polarized light. Berthellot (1862) derived second-order equations for the rates of ester formation and, shortly after, Harcourt observed that rates of reaction doubled for each 10 °C rise in temperature. Guldberg and Waage (1864-67) demonstrated that the equilibrium of the reaction was affected by the concentration ) of the reacting substance(s). By 1877 Arrhenius had derived the definition of the equilbrium constant for a reaction from the rate constants of the forward and backward reactions. Ostwald in 1884 showed that sucrose and ester hydrolyses were affected by H+ concentration (pH). 

In zone a of Figure 2.5, the kinetics are first order with respect to [S], that is to say that the rate is limited by the availability (concentration) of substrate so if [S] doubles the rate of reaction doubles. In zone c however, we see zero order kinetics with respect to [S], that is the increasing substrate concentration no longer has an effect as the enzyme is saturated zone b is a transition zone. In practice it is difficult to demonstrate the plateau in zone c unless very high concentrations of substrate are used in the experiment. Figure 2.5 is the basis of the Michaelis-Menten graph (Figure 2.6) from which two important kinetic parameters can be approximated ... 

For reactions in the gaseons phase, a general guideline in chemistry is that the rate of reaction doubles for every 10°C rise in temperatnre. 

Suppose, when the initial concentration of A is doubled and the initial concentration of B is kept constant, the rate of the reaction doubles. This implies that the rate of reaction is directly proportional to the concentration of A, so rate cc [A]. ... 

The mechanism of this elimination reaction may be regarded as being similar to that of the dehydrogenation reaction. Double-bond isomerization leads to formation of a species with both double bonds in the ring. This is then metalated and eliminates the alkyl group (A )-... 

I.3.3 Miscellaneous reactions. Double aldol condensation of phthalic dialdehyde with thieno azepinedione 114 results in a 60% yield of naphtho derivative 115 (Scheme 23 (1999PHA645)). 

In the second approach, allylboronation of 9 with 10 led to the predominant formation of 8a which was transformed to 6a (R = H). The allylic alcohols 5a and 5b prepared from 6a and 6b, respectively, were subjected to asymmetric epoxidations307, each with (-f)-DET and (—)-DET, to provide four diastereomers. One of them, 4b, was identical with degradation product 2. Note that in these reactions double stereodifferenlialion (see Section A.2.3.5.4.) is operating (for configurational assignment at C-15, see p431)244. 

With some catalyst systems, selectivity to primary metathesis products is near 100%, but side reactions (double-bond migration, dimerization, cyclopropanation, polymerization) often reduce selectivity. Such side reactions, such as oligomerization and double-bond shift over oxide catalysts, may be eliminated by treatment with alkali and alkaline-earth metal ions.26... 

For complex mechanisms such as ECE or other schemes involving at least two electron transfer steps with interposed chemical reactions, double electrodes offer a unique probe for the determination of kinetic parameters. Convection from upstream to downstream electrodes allows the study of fast homogeneous processes. The general reaction scheme for an ECE mechanism can be written... 

When black powder burns, the first portion to receive the fire undergoes a chemical reaction which results in the production of hot gas. The gas, tending to expand in all directions from the place where it is produced, warms the next portion of black powder to the kindling temperature. This then takes fire and burns with the production of more hot gas which raises the temperature of the next adjacent material. If the black powder is confined, the pressure rises, and the heat, since it cannot escape, is communicated more rapidly through the mass. Further, the gas- and heat-producing chemical reaction, like any other chemical reaction, doubles its rate for every 10° (approximate) rise of temperature. In a confined space the combustion becomes extremely rapid, but it is still believed to be combustion in the sense that it is a phenomenon dependent upon the transmission of heat. 

Further examples of the formation of carbocyclic and carbopolycyclic compounds from (Z)-vinyl iodides with triethylamine as base have been reported and as noted in the related bromide reactions, double-bond isomerization is commonly observed.92... 

Not all reactions are redox reactions. Only the ones in which electrons are transferred from one reactant to another are classified as redox reactions. Many single-displacement reactions, combination reactions, decomposition reactions, and combustion reactions are redox reactions. Double displacement reactions never involve the transfer of electrons and are not, therefore, redox reactions. Since acid-base reactions are just a special type of double displacement reaction, they cannot be redox reactions, either. 

Organic chemists use a common rule of thumb that the rate of a typical chemical reaction doubles as the temperature is increased by ten degrees. Assume that the constants A and Ea in Equation 1.24 do not change as the temperature changes. What must the value of Ea (called the activation energy) be for the rate to double as the temperature is raised from 25C to 35C ... 

Most chemical reactions give off heat and are classified as exothermic reactions. The rate of a reaction may be calculated by the Arrhenius equation, which contains absolute temperature, K, equal to the Celsius temperature plus 273, in an exponential term. As a general rule, the speed of a reaction doubles for each 10°C increase in temperature. Reaction rates are important in fires or explosions involving hazardous chemicals. A remarkable aspect of biochemical reactions is that they occur rapidly at very mild conditions, typically at body temperature in humans (see Chapter 3). For example, industrial fixation of atmospheric elemental nitrogen to produce chemically bound nitrogen in ammonia requires very high temperatures and pressures, whereas Rhizobium bacteria accomplish the same thing under ambient conditions. 

Metathesis reactions (double-replacement reactions)—chemical change that involves an exchange of positive ions between two compounds... 

Experiments show that doubling the concentration of methyl bromide, [CH3Br], doubles the rate of reaction. Doubling the concentration of hydroxide ion, [ OH], also doubles the rate. Thus, the rate is proportional to both [CH3Br] and [ OH], so the rate equation has the following form ... 

NO and C1N02 molecules that collide in the correct orientation, with enough kinetic energy to climb the activation energy barrier, can react to form N02 and C1NO. As the temperature of the system increases, the number of molecules that carry enough energy to react when they collide also increases. The rate of reaction therefore increases with temperature. As a rule, the rate of a reaction doubles for every 10 C increase in the temperature of the system. 

---