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The present invention relates to a process of preparing phenyl magnesium chloride. Although phenyl magnesium bromide has heretofore been known and used as a Grignard agent, its high cost has rendered its use non-attractive. (It is also watched in many countries. -VV) Consequently, it was believed that phenyl magnesium chloride could be prepared more economically thereby yielding a more desirable reagent. However, because of the extreme inertness of the aromatic chloride, the usual methods of preparing reagents in ether using chlorobenzene as a reactant were not succesful for the preparation of phenyl magnesium chloride. In the past, resort was made to extreme conditions of high temperature and pressure for a long period, but even under these conditions, disappointing yields were obtained. Such processes were objectionable, not only because of the poor yields of the desired reagent, but also because of the formation of tars as by-products which were difficult to remove.

It is an object of this invention to provide an economical process for the preparation of phenylmagnesium chloride involving the reaction of chlorobenzene and magnesium.

It has been found that the phenylmagnesium chloride may be prepared very readily by the reaction of chlorobenzene and magnesium through the use of an inorganic or organic catalyst containing an -NO₃ or -NO₂ group. More particularly the phenylmagnesium chloride may be prepared by reacting chlorobenzene with magnesium at reflux temperatures in the presence of catalytic amounts of inorganic or organic nitrates or organonitro compounds. The reflux temperatures may be of about 130-135°C and preferably of about 130-132°C. It has further been found that 0.5-5% of said catalyst, and preferably 1-2%, based on the weight of magnesium employed is sufficient to effect catalysis of the reaction of magnesium with chlorobenzene.
The catalysts that are useful in the present invention may be more particularly defined by the formula:

R(NO_x)_n._yH₂O

wherein x has a value of 2 or 3, n is the valence of group R, y is zero or a positive number and R is selected from the class consisting of H, metal element, metalloid element or an organic radical preferably aliphatic or carbocyclic organic radicals. The catalysts employed in this invention include nitric acid, metal and metalloid nitrates, organic nitrates and organonitro compounds containing one or more nitro or nitrate groups in their hydrated or non-hydrated form.

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Then the patent goes on to list half of all nitrates and nitro-compounds known to man, so to speak.

Interesting is:

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The degree of hydration may vary considerably. By way of illustration the number of molecules of water, bound as water of crystallization in the inorganic nitrate will vary from 0 to about 24 and preferably from 0 to about 6.

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Even more interesting is the following part:

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The raw materials utilized in the present invention were standard commercial products. The magnesium utilized in the present invention did not necessarily possess a clean, unoxidized surface, but could be old and dirty. The magnesium may be in the form of turnings (resulting from the milling of magnesium), granular material (produced on a hammer-mill), or in other comminuted forms.

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Well, hello there!! This means we can go very cheap here, and maybe use ning-style () ground up pencil sharpeners or similar.

And it doesn't stop here:

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Similarly, the chlorobenzene was not a pure product but contained the usual impurities found in the commercial products. Since chlorobenzene is usually prepared from industrial coal tar benzene, it is expected that small amounts of chlorothiophene may be present in the commercial product. On analysis, the chlorobenzene used was found to contain 0.18% sulfur. Likewise, the catalysts used in the present invention were ordinary untreated commercial products containing the usual impurities.

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Price of technical grade chlorobenzene : 5 euros per liter.

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A feature of the present invention is the utilization of reflux temperatures of about 130-135°C and preferably 130-132°C at atmospheric pressure. This temperature range overcomes the disadvantages arising from the prior methods wherein superatmospheric pressures and temperatures above about 150°C were employed. The violent reaction which could ensue as a result of such severe conditions results in charring and in the formation of tars. With the present invention, the reaction between chlorobenzene and magnesium is easily controlled. The non-exothermicity of this reaction renders it necessary to apply heat in order to obtain a reaction. It is possible by merely withdrawing the heat source to halt the reaction for a determined period of time after which further application of heat will permit the reaction to continue. As about 10 to 20 hours is necessary in order to obtain complete reaction between the magnesium and chlorobenzene, the removal of the source of heat permits halting of the reaction when desired and its resumption at a future time.

Another embodiment of the present invention resides in the advantageous use of a diluent or solvent during the reaction. It has been found that in the absence of a diluent, the reaction mixture becomes so viscious as to inhibit further reaction, thereby reducing the yield. It has also been found that charring occurs when no diluent is present during the reaction, thereby yielding an impure product. This solvent may be present at the beginning of the reaction or may be added to the reaction mixture at any time after the initiation of the reaction but before it has become unduly viscious. In view of the variety of catalyst and diluents useful herein, the last possible time for addition of the diluent must be determined separately for each material by simply observing the consistency of the mixture as the reaction progresses.
Suitable solvents or diluents include chlorobenzene, benzene, toluene, xylene, phenyl ether, mixtures thereof and the like. If more than one mole of chlorobenzene is present in the reaction mixture, the excess chlorobenzene acts as a diluent and no other solvent need to be added.

Another preferred embodiment of the present invention resides in carrying out the reaction under an inert atmosphere. Although this is not essential in the present process, the exclusion of air and its displacement by, for instance, nitrogen results in a shorter initiation period. Other suitable inert gasses include argon, krypton, neon and helium. By initiation period is meant the time from the beginning of reflux to the time the reaction actually commences. This period can generally vary over a range of about ten minutes to about one hour. However, when carrying out this reaction under nitrogen, an initiation period of only about twenty minutes to thirty-five minutes is observed as a result. Another deleterious effect of the oxygen in the air on the reagent is the formation of phenols as a result of air oxidation. Thus, while a nitrogen atmosphere is not essential in the present process, it does provide additional advantages in the obtention of phenylmagnesium chloride in high yield and purity.

Still another embodiment of the invention resides in efficient agitation of the reaction mixture. It has been found that stirring is essential to the obtention of a high yield of pure product. The absence of agitation may result in charring, a considerably longer initiation period and consequently a less economical process. The degree of agitation, namely, the speed of the stirrers, affects the rapidity of the reaction. More specifically, rapid agitation on the order of 10000 RPM allows the reaction to be complete three hours after reflux (130°C), whereas slow stirring, on the order of 100-200 RPM, may require 20 hours after reflux starts for completion. Furthermore, rapid agitation causes the reaction to commence before reflux temperatures of about 130°C are reached, reaction being noted at 110-118°C. Rapid agitation reduces the reaction period and is advantageous where rapidity of reaction is a desirable feature, but it is not essential in the present invention.

The phenylmagnesium chloride yields obtained by this process range from 75-95% based on the weight of magnesium as compared to prior processes wherein a maximum of only 50% by weight of magnesium has been obtained. This process affords a considerable saving, rendering the present process a commercially superior procedure for the manufacture of the phenylmagnesium chloride reagent. In addition, the catalytic initiation of the reaction between magnesium and chlorobenzene is brought about uniformity in ten to sixty-five minutes instead of the usual lengthy period.

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I'll include the first example here:

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24.3 gms (1 g atom) of magnesium turnings, 562.5 gms (5 moles) of commercial chlorobenzene, and 0.25 gm (1% by weight of the magnesium) of potassium nitrate (KNO₃) were charged into a one liter, 3-necked flask equipped with a stainless steel anchor stirrer, reflux condensor, a thermometer, and a Glas-col heater. All joints were glass. This mixture was stirred and heated to reflux. Thirty minutes after reflux began, a greenish colour developed in the mix indicating that the reaction had started. Heating was continued for 20 hours longer. The mixture was cooled, diluted with anhydrous ethyl ether and made up to one liter of solution in a volumetric flask by addition of more ether. The solution was shaken to disperse solids, allowed to settle for a moment, and a 20 ml sample was pipetted into a 500 ml Erlenmeyer flask containing 50 ml water and 50 ml of 0.5 H₂SO₄. The whole mixture was heated on a steam bath for thirty minutes. 1.5 ml of 0.04% bromocresol purple was used as an indicator for the back-titration with 0.2 N NaOH solution and the yield was calculated. This is the well-known Gilman titration, somewhat modified. The yield for this run (based on the average of 3 titrations) was 95.4% . If desired the phenylmagnesium chloride may be separated from excess chlorobenzene by destillation after the reaction is completed.

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I must add that this is one of the most detailed and well-written patents I've read so far. Thank you very much mr. Ramsden!