Yield of a product

The yield of a product is a measure of the reaction extent at some point (time or position) in terms of a specified product and reactant. The most direct way of calculating the yield of a product in a complex system from experimental data is by means of a stoichiometric model in canonical form, with the product as a noncomponent. This is because that product appears only once in the set of equations, as illustrated for each of CO, CO and HCHO in Example 5-1. 

Consider reactant A and (noncomponent) product D in the following set of stoichiometric equations  

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On evaporating the alcoholic solution under reduced pressure from a water bath held at 50-60° (Note 6) the residue weighs about 540 g. A mixture of 600 cc. of absolute alcohol and 10 cc. of concentrated sulfuric acid (Note 7) is then added. The mixture is then heated on the water bath under a reflux condenser for three hours. The excess of alcohol and some of the water formed are removed by distillation under reduced pressure and the residue again heated for two hours with 300 cc. of absolute alcohol and an additional 4 cc. of concentrated sulfuric acid. The alcohol is removed by distillation under reduced pressure, and when the ester has cooled to room temperature, the sulfuric acid is neutralized with a concentrated solution of sodium carbonate the ester (upper layer) is separated, and the aqueous solution extracted with ether, or preferably benzene about one-tenth of the yield is in the extract. The combined products are placed in a i-l. distilling flask and distilled under reduced pressure after the solvent and alcohol and water have been removed. The ester is collected at 94-990, chiefly at 97-98°/x6 mm. (Note 8). The yield of a product analyzing about 97-98 per cent ethyl cyanoacetate amounts to 474-492 g. (77-80 per cent of the theoretical amount) (Note 9). 

The theoretical yield of a product is the maximum quantity that can be expected on the basis of the stoichiometry of a chemical equation. The percentage yield is the percentage of the theoretical yield actually achieved. 

J 2 Identify the limiting reactant of a reaction and use the limiting reactant to calculate the yield of a product and the... 

Product quantum yields are much easier to measure. The number of quanta absorbed can be determined by an instrument called an actinometer, which is actually a standard photochemical system whose quantum yield is known. An example of the information that can be learned from quantum yields is the following. If the quantum yield of a product is finite and invariant with changes in experimental conditions, it is likely that the product is formed in a primary rate-determining process. Another example In some reactions, the product quantum yields are found to be well over 1 (perhaps as high as 1000). Such a finding indicates a chain reaction (see p. 895 for a discussion of chain reactions). 

In order to determine the product distribution quantitatively, it is necessary to combine material balance and reaction rate expressions for a given reactor type and contacting pattern. On the other hand, if the reactor size is desired, alternative design equations reflecting the material balances must be employed. For these purposes it is appropriate to work in terms of the fractional yield. This is the ratio of the amount of a product formed to the amount of reactant consumed. The instantaneous fractional yield of a product V (denoted by the symbol y) is defined... 

The fractional yield of a product is a measure of how selective a particular reactant is in forming a particular product, and hence is sometimes referred to as selectivity.1 Two ways of representing selectivity are (1) the overall fractional yield (from inlet to a particular point such as the outlet) and (2) the instantaneous fractional yield (at a... 

Variations in the conditions used for the nitrolysis of hexamine have a profound effect on the nature and distribution of isolated products, including the ratio of RDX to HMX. It has been shown that lower reaction acidity and a reduction in the amount of ammonium nitrate used in the Bachmann process increases the amount of HMX formed at the expense of Bachmann and co-workers ° were able to tailor the conditions of hexamine nitrolysis to obtain an 82 % yield of a mixture containing 73 % HMX and 23 % RDX. Continued efforts to provide a method for the industrial synthesis of HMX led Castorina and co-workers to describe a procedure which produces a 90 % yield of a product containing 85 % HMX and 15 % RDX. This procedure conducts nitrolysis at a constant reaction temperature of 44 °C and treats hexamine, in the presence of a trace amount of paraformaldehyde, with a mixture of acetic acid, acetic anhydride, ammonium nitrate and nitric acid. Bratia and co-workers ° used a three stage aging process and a boron trifluoride catalyst to obtain a similar result. A procedure reported by Picard " uses formaldehyde as a catalyst and produces a 95 % yield of a product containing 90 % HMX and 10 % RDX. 

Similar electrolysis without the divider affords 82% yield of a product containing 78% of 2,5-... 

In order to improve the relative yield of a product from complex reactions, a manufacturer may vary the operational procedure for the chosen reactor. In some cases, this amounts to changing the flow pattern. When more than one reactant is used, it may sometimes be advantageous to use more than one entry point for a tubular-flow reactor (see Fig. 6). Delbridge and Dyson [53] showed that, for the case where reaction (8) was accompanied by... 

Reaction of acetone with hydrogen sulfide in the presence of acidified ZnCl2 at 25° C gives a good yield of a product composed of60-70% hexamethyltrithiane and 30-40% of 2,2-propanedithiol. Thioacetone can be obtained by pyrolysis of either of these compounds. The trithiane is pyrolyzed either on quartz rings heated to 500-650° C at 5-20 mm (30) or by means of a hot wire (32). The dithiol is pyrolyzed on sodium fluoride pellets heated to 150° C at 11 mm (50). In both cases the pyrolysate is immediately collected in a trap cooled to — 78° C. 

The yield of a product P is defined as the amount of product divided by the amount of A fed (initial amount) ... 

Dose rate has little or no influence on the evolution of hydrogen from PET (Figure 5) nor, apparently, on the evolution of other gases (Table I). An indication that the yield of a product might depend on... 

The Catarole process was developed in England during the past 10 to 15 years for the production of aromatics (20). Placed in commercial operation in 1948, the process charges naphtha or gas oil over a catalyst at a high temperature to obtain a 40 to 60% yield of a product containing up to 95% aromatics. A complete range of aromatic compounds from benzene to polycyclic aromatics is produced (17). 

The moist cake is mixed with 27 g. of zinc dust and 300 cc. of glacial acetic acid in a x-1. round-bottom flask, and the mixture is refluxed vigorously for about four hours (Note 4). When the reduction is complete, the mixture is cooled and filtered with suction. The filter cake is washed once with water and then transferred to a i-l. beaker. The cake is suspended in 200 cc. of water and the suspension is heated to boiling. The hot solution is made strongly alkaline by the addition of about 40 cc. of 33 per cent aqueous sodium hydroxide solution. The alkaline solution is boiled for about twenty minutes to insure complete extraction of the product from the filter cake, filtered from the insoluble material (Note 5) and the thiosalicylic acid is then precipitated by the addition of sufficient concentrated hydrochloric acid to make the solution acid to Congo red paper. The product is filtered with suction, washed once with water and dried in an oven at 100-110°. The yield of a product which melts at 162-163° is 110-130 g. (71-85 per cent of the theoretical amount based on the anthranilic add). 

Uramil is a fine, white powder which becomes pink to red on standing. The yield of a product which does not melt below 400° is 40-46 g. (63-73 per cent of the theoretical amount). 

In practical applications, where the maximum yield of a product or electricity in electrochemical energy conversion systems at the lowest energy cost is desirable, the rate of mass transport should be fast enough in order not to limit the overall rate of the process. For electroanalytical applications, such as polarography or gas sensors, on the other hand, the reaction must be limited by the transport of the reactant since the bulk concentration which is of interest is evaluated from the limiting con-vective-diffusional current. 

Bargellini and Martegiani 2 used 73 per cent sulfuric acid and heated on the water bath. They obtained an improved yield of a product of better quality. Zinc chloride in acetic acid proved to be unsatisfactory. 

Treatment of quinolizinium bromide with two equivalents of piperidine gives a high yield of a product A, C14H18N2. Reaction of A with phenacyl bromide followed by quenching of the reaction mixture with water gives a product B which was originally claimed to be 3-benzoyl-2-vinylindolizine. Subsequent reinvestigation of the structure of B, however, showed that it was in fact 3-(2-phenyl-l-indolizinyl)prop-2-ene-l-al 1. 

Condensation of the pyrrolidine enamine of cyclohexanone with l,l-dicyano-2,2-dimethylcyclopropane proceeds smoothly in refluxing dry xylene and gives the expected adduct in 76% yield. Recrystallisation of the adduct from 95% ethanol, however, gave a 91% yield of a product which no longer contained the pyrrolidine group but whose spectral data clearly showed the presence of a ketone group and an enaminonitrile function. Hydrolysis of this latter product with phosphoric acid/acetic acid gave 5-(2-oxo-4,4-dimethylcyclopentyl)pentanoic acid in 83% yield. 

The usual method of preparing iodine trichloride by subliming iodine into a current of chlorine gas is tedious and gives a poor yield of a product contaminated with iodine and iodine monochloride. Furthermore, the product deposits on the sides of the flask in crusts which are difficult to remove. 

The following data give the yields of a product that resulted from trying catalysts from four different suppliers in a process. Deter-... 

Figure 1.107 Relation between yield of a product R and conversion of a reactant A for different rate constants and lamination widths for one selected scenario of elemental reaction (two reactants A + B form R, while B can react with R as well in a consecutive reaction to the consecutive product S). W lamellae width k rate constant cf> ratio of reaction rate to diffusion rate [129] (by courtesy of Elsevier Ltd.).

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