US3641080A - Process for preparing dialkylizinc compounds from alkylbromide and alkyliodide - Google Patents

Process for preparing dialkylizinc compounds from alkylbromide and alkyliodide Download PDF

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Publication number
US3641080A
US3641080A US792845*A US3641080DA US3641080A US 3641080 A US3641080 A US 3641080A US 3641080D A US3641080D A US 3641080DA US 3641080 A US3641080 A US 3641080A
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zinc
alloy
mixture
reaction
sodium
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English (en)
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Schrade F Radtke
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International Lead Zinc Research Organization Inc
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International Lead Zinc Research Organization Inc
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
    • C07F3/00—Compounds containing elements of Groups 2 or 12 of the Periodic Table
    • C07F3/06—Zinc compounds

Definitions

  • This invention relates to a direct process for preparing dialkylzinc compounds.
  • Diorganozinc compounds are generally prepared by two methods.
  • the first method reacts a zinc halide with a reactive organomet'allic, such as lithium or magnesium, in an ether solvent.
  • the second method involves a direct synthesis starting from metallic zinc or zinc alloys with alkyliodides. Mixtures of alkyl bromides and iodides have also previously been used in combination with zinc-copper alloy.
  • the first method is disadvantageous in that it requires two separate steps to be performed. In the first step the lithium or magnesium reagent must be formed, and in the second step the actual formation of the organozinc compound takes place.
  • An additional disadvantage is the presence in the reaction of flammable solvents. The separation of the solvents from the product is not always easily achieved, especially with the utilization of lower alkyls.
  • the second method is more attractive in that only one step is required and the use of solvents is not necessary, although recent attempts to find improved conditions have utilized solvents with high dielectric constants, such as dimethylformamide.
  • solvents with high dielectric constants such as dimethylformamide.
  • the use of solvents makes it impossible to separate solvent from the product.
  • the reactions are performed by refluxing finely divided zinc alloy with alkylbromide and alkyliodide.
  • the reaction should be carried out in the absence of moisture, and therefore an inert atmosphere is preferred, such as nitrogen, argon, or carbon dioxide.
  • the reactions may be carried out at atmospheric pressure, unless the starting materials are too volatile, in which case pressure should be applied. This may be necessary with mixtures of MeBr and MeI.
  • the molar ratios of alkylbromide to alkyliodide may range from 1:1 to 20: 1. Good results were obtained using ratios of 1:1 to 5:1 alkylbromide to alkyliodide. Due to the lower cost of the alkylbromide, however, ratios of 3 :1 and above are most preferred.
  • the reaction usually begins a few minutes after the starting materials have made contact with each other, especially if substantially all traces of moisture have been removed from the atmosphere and the apparatus. Heating of the reaction mixture may be necessary to begin the reaction, but if the reaction is exothermal refluxing temperature is maintained without the application of external heat. In the event that the reaction is not exotherrnal, external heating may be applied to maintain the reflux temperature. It has been found that a temperature in the range of 40 -1 C. is satisfactory. A temperature range of 140 C. is preferred.
  • the reaction is considered complete when refluxing stops.
  • the flask is connected with a distilling head and the contents of the flask are distilled under reduced pressure to recover the dialkylzinc compound.
  • the zinc alloys which have proved themselves reliable for purposes of the invention are the lithium, potassium and sodium alloys.
  • the alloys may be formed by fusing the metals together in a steel crucible under an inert atmosphere, for example, argon. The cooled melt is machined to fine particle size. Usually turnings may be used, but if the alloy is very brittle a sandlike material is obtained upon machining.
  • the shot method may also be utilized to prepare the alloys on an industrial scale.
  • the maximum amount of sodium which can be alloyed with zinc is one atom of. sodium per twelve atoms of zinc. This corresponds with an alloy containing three wt. percent sodium, the balance being zinc.
  • Table I contains data showing the yield of dialkylzinc in relation to the percentage of sodium in the alloy.
  • dialkylzinc decreases as the sodium content of the alloy decreases.
  • the 2% sodium/zinc alloy gives, however, no significantly lower yields than the 3% sodium/zinc alloy.
  • the zinc alloy containing as little as 1% sodium also gives good results with the alkylbromide.
  • the yields of dialkylzinc gradually decreases to those obtained using pure zinc.
  • the percentage of sodium lie between 2 and 3 wt. percent.
  • Zinc alloyed with potassium is obtained by fusing zinc and potassium under an inert atmosphere, such as nitrogen, and machining in the usual way.
  • the alloy is very reactive and should be kept in an inert atmosphere.
  • the maximum amount of. potassium in the zinc/potassium alloy is approximately 5 wt. percent, which corresponds to a molar ratio of 12 moles zinc to 1 mole potassium.
  • the reaction with the alkylbromide and alkyliodide mixture is carried out in the same manner as with the zinc/sodium alloy. Once begun, the reaction continues spontaneously upon addition of the bromide and iodide.
  • the potassium content of the alloy may be reduced without loss of activity.
  • the zinc/potassium alloys are easily handled and machined to small particle size.
  • the 2% potassium/zinc alloy is well suited for the direct synthesis of zinc dialkyls, although the yields in general are somewhat lower than for the zinc/sodium alloys.
  • the recommended range would be 0.5-5.0 wt. percent potassium with 1.5 to 2.0 wt. percent potassium preferred.
  • a useful lithium range is -1 to wt. percent lithium in the zinc alloy, with a preferred content of approximately 2. wt. percent lithium.
  • Ternary alloys may be used to provide good yields of dialkylzinc compounds.
  • the amalgamation of the zinc/ sodium alloy by treating the 3% sodium/zinc alloy with HgCl in tetrahydrofuran provides approximately the same yield as using the zinc/sodium alloy without the HgCl
  • An alloy composed of 2.6% sodium, 1.1% mercury and the rest zinc was reacted with a 1:1 ratio of EthBr/ EthI and yielded 71% diethylzinc.
  • the synthesis according to the invention may be carried outwith both normal and branched chain alkylbromides and iodides. Since longer chain dialkylzincs, for example, where R is greater than C have limited thermal stability, a direct synthesis is not practical. At the other end of the scale, the boiling points of methylbromide and methyliodide are low and require reaction under higher pressure conditions than a mo pheri p re.
  • a process for preparing dialkylzinc compounds comprising:
  • an alloy of zinc having at least one metal selected from the group consisting of sodium, potassium and lithium, the amount of metal in the alloy comprising about 1 to about 3 weight percent sodium, about 0.5 to about 5.0 weight percent potassium and about 1 to about 10 weight percent lithium, with the remaining percentage being zinc, with (ii) a mixture of alkylbromide and -alkyliodide in a molar ratio of at least 1:1 zinc to the alkylbromide and alkyliodide mixture, the molar ratio of the bromide to iodide lying between about 5:1 and about 20:1, the alkyl radical being selected from the group consisting of saturated and unsaturated alkyl radicals containing from 1 to 8 carbon atoms; and
  • dialkylzinc is added to the reaction mixture to remove traces of moisture.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
US792845*A 1969-01-21 1969-01-21 Process for preparing dialkylizinc compounds from alkylbromide and alkyliodide Expired - Lifetime US3641080A (en)

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US79284569A 1969-01-21 1969-01-21

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US3641080A true US3641080A (en) 1972-02-08

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US (1) US3641080A (fr)
BE (1) BE733887A (fr)
FR (1) FR2028750A1 (fr)
GB (1) GB1242789A (fr)
NL (1) NL6908448A (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4385003A (en) * 1981-10-30 1983-05-24 Stauffer Chemical Company Dialkylzinc composition having improved thermal stability
US4402880A (en) * 1981-10-30 1983-09-06 Stauffer Chemical Company Dialkylzinc compositions having improved thermal stability
US4407758A (en) * 1981-10-30 1983-10-04 Stauffer Chemical Company Dialkylzinc compositions having improved thermal stability

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4385003A (en) * 1981-10-30 1983-05-24 Stauffer Chemical Company Dialkylzinc composition having improved thermal stability
US4402880A (en) * 1981-10-30 1983-09-06 Stauffer Chemical Company Dialkylzinc compositions having improved thermal stability
US4407758A (en) * 1981-10-30 1983-10-04 Stauffer Chemical Company Dialkylzinc compositions having improved thermal stability

Also Published As

Publication number Publication date
BE733887A (fr) 1969-11-03
FR2028750A1 (fr) 1970-10-16
GB1242789A (en) 1971-08-11
NL6908448A (fr) 1970-07-23

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