Double-displacement reaction

Precipitation reactions, such as the ones we will see in this section, belong to a general class of reactions called double-displacement reactions. (Double displacement reactions are also called double-replacement, double-exchange, or metathesis reactions.) Double displacement reactions have the following form, signifying that the elements in two reacting compounds change partners. 

Ammonium perchlorate is a colorless, crystalline compound having a density of 1.95 g/mL and a molecular weight of 117.5. It is prepared by a double displacement reaction between sodium perchlorate and ammonium chloride, and is crystallized from water as the anhydrous salt. 

Reactions that fit this model are called ping-pong or double-displacement reactions. Two distinctive features of this mechanism are the obligatory formation of a modified enzyme intermediate, E, and the pattern of parallel lines obtained in double-reciprocal plots (Figure 14.19). 

Maltose phosphorylase proceeds via a single-displacement reaction that necessarily requires the formation of a ternary maltose E Pi (or glucose E glucose-l-phosphate) complex for any reaction to occur. Exchange reactions are a characteristic of enzymes that obey double-displacement mechanisms at some point in their catalysis. 

The antibiotic activity of certain (3-lactams depends largely on their interaction with two different groups of bacterial enzymes. (3-Lactams, like the penicillins and cephalosporins, inhibit the DD-peptidases/transpeptidases that are responsible for the final step of bacterial cell wall biosynthesis.63 Unfortunately, they are themselves destroyed by the [3-lactamases,64 which thereby provide much of the resistance to these antibiotics. Class A, C, and D [3-lactamases and DD-peptidases all have a conserved serine residue in the active site whose hydroxyl group is the primary nucleophile that attacks the substrate carbonyl. Catalysis in both cases involves a double-displacement reaction with the transient formation of an acyl-enzyme intermediate. The major distinction between [3-lactamases and their evolutionary parents the DD-peptidase residues is the lifetime of the acyl-enzyme it is short in (3-lactamases and long in the DD-peptidases.65-67... 

When acids and bases come into contact with one another, a chemical reaction called a neutralization reaction takes place. A neutralization reaction is a double displacement reaction. In a double displacement reaction, the positive ions from one reactant take the place of the positive ions in the other reactant. For example, if hydrochloric acid and sodium hydroxide react with one another, the positive sodium ion in sodium hydroxide will take the place of the hydrogen ion in the hydrochloric acid ... 

Remember that an acid-base reaction is a double displacement reaction. Therefore, if sulfuric acid and potassium hydroxide are mixed, the positive ions trade places. The hydrogen ions from the sulfuric acid will react with the negative hydroxide ions to form water. Because a hydrogen ion has a charge of + 1 and a hydroxide ion has a charge of -1, they bond in a 1 1 ratio ... 

Because this is a reaction between an acid and a base, it will be a double displacement reaction, and the positive ions will switch places. The potassium ion will react with the sulfate ion, forming the salt potassium sulfate (K2S04). And the hydrogen ion in the acid will react with the hydroxide ion in the base to form HOH, or water (H20). 

Double displacement reaction A chemical reaction in which the positive ion in one reactant takes the place of the positive ion in the other reactant. 

The displacement reaction of a vicinal bis(imidazolesulfonate) via the bisiodide has been used for double deoxygenation of methyl 4,6-O-benzylidene-jS-D-galactopyrano-side [11]... 

For either of the ternary complex mechanisms described above, titration of one substrate at several fixed concentrations of the second substrate yields a pattern of intersecting lines when presented as a double reciprocal plot. Hence, without knowing the mechanism from prior studies, one can not distinguish between the two ternary complex mechanisms presented here on the basis of substrate titrations alone. In contrast, the data for a double-displacement reaction yields a series of parallel lines in the double reciprocal plot (Figure 2.15). Hence it is often easy to distinguish a double-displacement mechanism from a ternary complex mechanism in this way. Also it is often possible to run the first half of the reaction in the absence of the second substrate. Formation of the first product is then evidence in favor of a doubledisplacement mechanism (however, some caution must be exercised here, because other mechanistic explanations for such data can be invoked see Segel, 1975, for more information). For some double-displacement mechanisms the intermediate E-X complex is sufficiently stable to be isolated and identified by chemical and/or mass spectroscopic methods. In these favorable cases the identification of such a covalent E-X intermediate is verification of the reaction mechanism. 

Figure 1.43 indicates major sites of reactivity within the ring structures for nucleophilic displacement reactions. Cytosine, thymine, and uracil all react toward nucleophilic attack at the same two sites, the C-4 and C-6 positions. The presence of powerful nucleophiles, even at neutral pH, can lead to significant base modification or cleavage with pyrimidine residues (Debye, 1947). For instance, hydrazine spontaneously adds to the 5,6-double bond, initiating further ring reactions,... 

The metathesis (also called double displacement) reactions are those in which the positive and negative ions in two compounds "change partners," with no change in oxidation numbers, to form two new compounds. There are three ... 

A (a) This is a metathesis or double displacement reaction. Elements do not change oxidation states during this reaction. It is not an oxidation-reduction reaction. 

Copper(n) sulfate, CUSO4, reacts with sodium hydroxide, NaOH, in a double displacement reaction. A precipitate of copper(n) hydroxide, Cu(OH)2, and aqueous sodium sulfate, Na2S04, is produced. 

In Chapter 9, as in most of Unit 4, you learned about equilibrium reactions. In this section, you analyzed precipitation reactions. You mainly examined double-displacement reactions—reactions in which two soluble ionic compounds react to form a precipitate. You used the solubility product constant, Ksp, to predict whether or not a precipitate would form for given concentrations of ions. In Unit 5, you will learn about a class of reactions that will probably be new to you. You will see how these reactions interconvert chemical and electrical energy. 

In your previous chemistry course, you classified reactions into four main types synthesis, decomposition, single displacement, and double displacement. You also learned to recognize combustion reactions and neutralization reactions. You have now learned to classify redox reactions. In addition, you have also learned about a special type of redox reaction known as a disproportionation reaction. 

A double displacement reaction (27) was shown to occur with aryl benzoates (Van Etten, 1967b). 

An enzyme-catalyzed double-displacement reaction mechanism in which two substrates react to form two products, but one product must be released before the second substrate binds to the enzyme. 

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