Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C18/00—Alloys based on zinc
• • 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.
• Diorganic compounds are generally prepared by two methods.
• the first method reacts a zinc halide with a reactive organometallic, such as lithium or magnesium, in an ether solvent.
• the second method involves a direct synthesis starting from metallic zinc or zinc alloys with alkyl iodides. Mixtures of alkyl bromides and iodides have also previously been used in combination with zinccopper 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 ealiilly achieved, especially with the utilization of lower a ys.
• 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 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 exothermal, external heating may be applied to maintain the reflux temperature. It has been found that a temperature in the range of 40-l80 C. is satisfactory. A temperature range of l00-l40 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. Distillation of the product mixture vaporizes the dialkylzinc compound which is captured as a distillation product.
• 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.
• 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/potas sium 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 is carried out in the same manner as with the zinc/sodium alloy. Once begun, the reaction continues spontaneously upon addition of the bromide.
• 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 butyl'brornide and yielded 52% dibutylzinc.
• the synthesis according to the invention may be carried out with both normal and branched chain alkylbromides. Since longer chain dialkylzincs, for example, where R is greater than C have limited thermal stability, a direct synthesis involving thermal cracking of primarily formed RZnBr to give R Zn+ZnBr is not practical. At the other end of the scale, the boiling point of methyl bromide is low and requires reaction under higher pressure conditions than atmospheric pressure.
• Hg contained some 2,7-dimethyloctane (the Wurtz coupling product of iso-amylbromide) as, appeared from a gas chromatoe graphic analysis of the hydrolysis products).
• the yield of di-isoamylzinc after refractionation, B.P. 64-,689/ 2 mm.) was 5.48 g. (46% of theory).
• EXAMPLE 5 I 1 n-Bu Zn from ZnK alloy (2% K) and n-BuBr A mixture of 29.0 g. of finely divided Zn-2.0 K. alloy (0.44 g. at. Zn) and 5.0 ml. of n-BuBr was gradually warmed up (to oil bath temp, of When reaction had started -18 ml. of n-BuBr (0.22 mole n"-BuBr.in total)v was added dropwise' After a further 30 min hea'ting period 10.8 g. n-Bu Zn (55% of theory) was isolated by distillation in vacuo.
• 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 being 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 reagent consisting essentially of alkylbromide in a molar ratio of at least 1 to 1, zinc to alkylbromide, wherein the alkyl radical is selected from the group consisting of saturated and unsaturated alkyl radicals containing from 1 to -8 carbon atoms; and
• alkylbromide is selected from the group consisting of methylbromide and ethylbromide, and the alkylbromide is re fiuxed under a pressure above that of atmospheric pressure.
• dialkylzinc is added to the reaction mixture to remove traces of moisture.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

Country Status (6)

Cited By (6)

• 1969
  • 1969-01-21 US US792852*A patent/US3641081A/en not_active Expired - Lifetime
  • 1969-05-19 BE BE733267D patent/BE733267A/xx unknown
  • 1969-05-20 DE DE19691925652 patent/DE1925652A1/de active Pending
  • 1969-05-22 NL NL6907898A patent/NL6907898A/xx unknown
  • 1969-05-28 GB GB26884/69A patent/GB1243305A/en not_active Expired
  • 1969-06-20 FR FR6920828A patent/FR2028746A1/fr not_active Withdrawn

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