The Heat of Reaction

Dissolve 10 g. of salicylic acid (o-hydroxybenzoic acid) in 7 ml. of dry pyridine contained in a too ml. conical flask. Then without delay (since this solution if allowed to stand tends to become a semi-solid mass) run in 7 5 ml. (8 3 g.) of acetyl chloride, adding about i ml. of the chloride at a time, and shaking the mixture continuously during the addition. The heat of the reaction causes the temperature of the mixture to rise rapidly ... 

A considerable amount of the formic acid, however, still remains behind in the distilling-flask as the unhydrolysed monoformate. Therefore, if time allows, dilute the residue in the flask with about an equal volume of water, and then steam-distil, the monoformate ester being thus completely hydrolysed and the formic acid then driven over in the steam. Collect about 400 ml. of distillate. Add this distillate to that obtained by direct heating of the reaction mixture and then treat with lead carbonate as described above. Total yield of lead formate is now about 40 g. 

The solution of the aniline hydrochloride should be cooled to 5°C., and this temperature maintained throughout the addition of the sodium nitrite solution. External cooling has to be maintained, otherwise the heat of the reaction would cause the temperature to rise, with the consequent decomposition of the diazonium chloride and the production of phenol. If, on the other hand, the temperature is reduced to about o , diazotisation becomes extremely slow and unchanged nitrous acid may remain in the solution for an impracticably long time. 

Place 30 ml. of ethanol in a 200 ml. conical flask fitted to a reflux water-condenser, and then add 1-4 g. of sodium cut into small pieces. The sodium rapidly dissolves to give a solution of sodium ethoxide, the ethanol boiling under the heat of the reaction. When the sodium has completely dissolved, detach the flask and cool it in ice-water. 

While the sodium ethoxide solution is cooling, prepare a solution of 7 7 g. of finely powdered iodine in 60 ml. of ether. When this solution is ready, add 9 ml. (9 6 g.) of ethyl malonate to the ethanolic sodium ethoxide solution, mix w ell and then allow to stand for 30-60 seconds not longer) then cautiously add the ethereal solution of the iodine, mixing thoroughly during the addition in order to avoid local overheating by the heat of the reaction. (If, after the ethyl malonate has been added to the sodium ethoxide, a considerable delay occurs before the iodine is added, the yield of the final product is markedly decreased.)... 

IsoValeric acid. Prepare dilute sulphuric acid by adding 140 ml. of concentrated sulphuric acid cautiously and with stirring to 85 ml. of water cool and add 80 g. (99 ml.) of redistilled woamyl alcohol. Place a solution of 200 g. of crystallised sodium dicliromate in 400 ml. of water in a 1-litre (or 1-5 litre) round-bottomed flask and attach an efficient reflux condenser. Add the sulphuric acid solution of the isoamyl alcohol in amaU portions through the top of the condenser shake the apparatus vigorously after each addition. No heating is required as the heat of the reaction will suffice to keep the mixture hot. It is important to shake the flask well immediately after each addition and not to add a further portion of alcohol until the previous one has reacted if the reaction should become violent, immerse the flask momentarily in ice water. The addition occupies 2-2-5 hours. When all the isoamyl alcohol has been introduced, reflux the mixture gently for 30 minutes, and then allow to cool. Arrange the flask for distillation (compare Fig. II, 13, 3, but with the thermometer omitted) and collect about 350 ml. of distillate. The latter consists of a mixture of water, isovaleric acid and isoamyl isovalerate. Add 30 g. of potassium not sodium) hydroxide pellets to the distillate and shake until dissolved. Transfer to a separatory funnel and remove the upper layer of ester (16 g.). Treat the aqueous layer contained in a beaker with 30 ml. of dilute sulphuric acid (1 1 by volume) and extract the liberated isovaleric acid with two... 

Method 2. Place a 3 0 g. sample of the mixture of amines in a flask, add 6g. (4-5 ml.) of benzenesulphonyl chloride (or 6 g. of p-toluenesulphonyl chloride) and 100 ml. of a 5 per cent, solution of sodium hydroxide. Stopper the flask and shake vigorously until the odour of the acid chloride has disappeared open the flask occasionally to release the pressure developed by the heat of the reaction. AUow the mixture to cool, and dissolve any insoluble material in 60-75 ml. of ether. If a solid insoluble in both the aqueous and ether layer appears at this point (it is probably the sparingly soluble salt of a primary amine, e.g., a long chain compound of the type CjH5(CH2) NHj), add 25 ml. of water and shake if it does not dissolve, filter it off. Separate the ether and aqueous layers. The ether layer will contain the unchanged tertiary amine and the sulphonamide of the secondary amine. Acidify the alkaline aqueous layer with dilute hydrochloric acid, filter off the sulphonamide of the primary amine, and recrystaUise it from dilute alcohol. Extract the ether layer with sufficient 5 per cent, hydrochloric acid to remove all the tertiary amine present. Evaporate the ether to obtain the sulphonamide of the secondary amine recrystaUise it from alcohol or dilute alcohol. FinaUy, render the hydrochloric acid extract alkaline by the addition of dilute sodium hydroxide solution, and isolate the tertiary amine. 

Aluminum trifluoride trihydrate [15098-87-0], AIF. -3H20, appears to exist in a soluble metastable a-form as well as a less soluble P-form (3). The a-form can be obtained only when the heat of the reaction between alumina and hydrofluoric acid is controlled and the temperature of the reaction is kept below 25°C. Upon warming the a-form changes into a irreversible P-form which is insoluble in water and is much more stable. The P-form is commercially available. 

Properties. Silver difluoride melts at 690°C, bods at 700°C, and has a specific gravity of 4.57. It decomposes in contact with water. Silver difluoride may react violently with organic compounds, quite often after an initial induction period. Provisions must be made to dissipate the heat of the reaction. Small-scale experiments must be mn prior to attempting large-scale reactions. 

The above equations for heat transfer apply when there is no heat generation or absorption during the reaction, and the temperature difference between the solid and the gas phase can be simply defined tliroughout the reaction by a single value. Normally this is not the case, and due to the heat of the reaction(s) which occur tlrere will be a change in the average temperature with time. Furthermore, in tire case where a chemical reaction, such as the reduction of an oxide, occurs during the ascent of tire gas in the reactor, the heat transfer coefficient of the gas will vary with tire composition of tire gas phase. 

The solution does not become homogeneous until it is warmed by the heat of the reaction. 

In a 2-1. round-bottomed, 3-necked flask fitted with a stirrer and two large-bore condensers are placed 200 cc. of 50 per cent nitric acid and 0.25 g. of vanadium pentoxide. The flask is heated to 65-70° in a water bath (thermometer in water), and I cc. of cyclopentanone added. Oxidation is indicated by the production of brown fumes. The water bath is removed, and 42 g. (less the i cc.) of the cyclic ketone added from a dropping funnel through the condenser at the rate of a drop every three seconds. The heat of the reaction keeps the flask at about 70°. If the temperature drops, oxidation ceases until the ketone has accumulated, when it may proceed almost explosively. In such a case, or if the temperature is higher, much succinic acid is formed. After addition has been completed, the water bath... 

In this example we selected a final outlet temperature of 100°F, This would be sufficiently low if the gas were only going to be compressed and dehydrated. For our case, we must also treat the gas for H2S and COt removal (Chapter 7). If we chose an amine unit, which we will in all likelihood, the heat of the reaction could heat the gas more than 10° to 20 T. making the next step, glycol dehydration, difficult (Chapter 8). In such a case, it may be better to cool the gas initially to a lower temperature so that it is still below 110°F at the glycol dehydrator. Often this is not possible, since cooling water is not available and ambient air conditions are in the 95°F to 1()0°F range. If this is so, it may be necessary to use an aerial cooler to cool the gas before treating, and another one to cool it before dehydration. 

The potassium cyanide is heated in an iron dish over a large burner until it begins to fuse, when 140 grains of red o.xide of lead are gradually added in small quantities and stirred in. The heat of the reaction causes the mass to melt... 

N Alkylation of 16 with benzyl bromide also occurs, and further heating of the reaction mixture leads to the C-alkylated product (25), probably by an intermolecular mechanism (33). 

Polymerizing ethylene can occur either in a tubular or in a stirred autoclave reactor. In the stirred autoclave, the heat of the reaction is absorbed by the cold ethylene feed. Stirring keeps a uniform temperature throughout the reaction vessel and prevents agglomeration of the polymer. 

Hydride ion-water reaction. As water is dropped onto solid calcium hydride, the hydride ion (H ) reacts immediately and vigorously to form H g) (which is ignited by the heat of the reaction) and OH-. 

We see that when a reaction can be expressed as the algebraic sum of a sequence of two or more other reactions, then the heat of the reaction is the algebraic sutn of the heats of these reactions. This generalization has been found to be applicable to every reaction that has been tested. Because the generalization has been so widely tested, it is called a law—the Law of Additivity of Reaction Heats. ... 

The relationship between activation energies for the forward and reverse reactions can be expressed mathematically. The activation energy is denoted by the symbol A// (read delta-//-cross ) and the heat of the reaction by AH. Hence we may write ... 

Before energy balance is calculated, we need to make mass balance. Figure 9.1 shows the material balance for ethanol and glycerol fermentation. Put simply, mass into the system is equal to mass out of die system. The mass of carbon dioxide is calculated by adding mass of dry cell, mass of glycerol, mass of edianol and mass of water at product stream and then subtracting die sum from die feed stream. As a result, die mass of carbon dioxide is defined. The heat of the reaction is calculated by the following equation ... 

The internal energy, U, of an ion which is formed in a stripping reaction is equal to the sum of the relative kinetic energy (according to Equation 11) plus the heat of the reaction W if W does not appear as... 

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