Temperature changes along the reactor
Optimized reaction conditions and achieved mobile yields for the lab-scale synthesis of benzyl RZnX reagents (starting material 0.5 moles/liter)
In order to expand the portfolio of continuously producible zinc carbonyls, the staff investigated not only benzyl starting materials, but also aliphatic compounds and a Reformatsky reagent
Optimized reaction conditions and flow yields of different RZnX reagents synthesized on a laboratory scale with a starting material of 0.5 mol/l
Organozinc compounds were also synthesized in high yields with few by-products, which was confirmed by gas chromatographic analysis. On this basis, a solution of 2.0 M starting material was converted for the first time using a laboratory reactor. No solubility limitations were observed for the zinc organics. It may be possible to obtain higher concentrations of RZnX if the right combination of solvents is used. the implementation of the zinc supplementation device was also successful. This allowed for multiple hours of fully continuous operation by providing fresh zinc during the synthesis. This is especially important for long term synthesis or conversion of higher concentration starting solutions (such as the 2.0 M solution studied), otherwise the mass of zinc in the reactor would not be sufficient to complete the conversion of the organohalides at a constant flow rate. In addition, by providing fresh zinc, the volume of the reactor can be better utilized, as the excess zinc will remain at a uniformly high level, while the free volume will remain at a low level.
The synthesis of highly concentrated zinc carbonyl chloride was investigated. A number of organozinc reagents prepared from 2.0 M starting material at concentrations four times the concentration of previously used solutions are provided.
Optimized reaction conditions and flow yields of selected RZnX reagents synthesized on a laboratory scale with a starting material of 2.0 mol/L
The sequential synthesis technique has successfully produced, for the first time, several classes of zinc organic compounds at high concentrations and in good to excellent yields, and there may be scope for further concentration increases, particularly if co-solvents are used.
The results of the laboratory syntheses indicate that most zinc reagents can be produced in good or even very good yields if the reaction parameters for certain compounds are adjusted and the solvents are changed. In addition, depending on the starting material, shorter residence times are sufficient for complete conversion of the used organohalides, which, combined with good or even very good yields, results in high productivity of organic zinc.
Pilot scale studies
Following laboratory synthesis, the conversion of some selected compounds was transferred to pilot scale. Complete conversion of the organohalides was achieved for most of the reagents. Yields were essentially comparable to those of the laboratory syntheses. The yields of the pilot scale syntheses were high, especially for the reactive starting materials. The results show that a wide range of different organozinc compounds can be obtained with the technology developed at the Fraunhofer Institute for International Metals Research. The synthesis process can be optimized quickly and easily with a high degree of flexibility. The efficiency of the reactor technology used is emphasized by the extremely high conversion rates of the highly concentrated starting materials. For the first time, high concentrations of zinc carbonyls have been successfully synthesized in succession.
Like the laboratory reactor, the pilot reactor for the synthesis of zinc organicl was fabricated from selectively laser-melted stainless steel. The pilot reactor consists of a cylinder filled with zinc pellets and a zinc replenishment unit which provides fresh zinc during the synthesis. If two reactor cartridges are used, as in the case of the synthesis shown in Fig. 3, the molar excess of zinc in the reactor is about 260 if a 0.5 M solution of organic halide is used.
Pilot-scale reactor setup with two cartridges for the continuous synthesis of RZnX reagents with synthesis efficiencies up to 300 ml/minute
The activation method is a chemical activation method already used in laboratory synthesis. The vibrations are transmitted from the slow-moving motor to the zinc bed via capillaries in the zinc packing. On the one hand, the capillary tube ensures that the zinc packing is compacted, on the other hand, the capillary tube provides space for a thermocouple to measure the temperature of the zinc packing bed during the synthesis.
Organozinc compounds produced on a pilot scale are listed. Conversion rates and yields were determined as in the laboratory synthesis. This example shows that with continuous processing and the reactor system shown here, various parameters can be easily tested in a single run, making optimization of the synthesis much easier.
Optimized reaction conditions and flow yields of selected RZnX reagents synthesized on a pilot scale, starting material 0.5 mol/l
In order to confirm the successful pilot scale synthesis of highly concentrated compounds, the conversion of 1.5 M benzyl bromide solution in the pilot reactor was investigated. The results are shown in Table 5.
Optimized reaction conditions and achieved mobile yields of 1.5 M benzyl zinc bromide solution for pilot scale synthesis
Summarization.
This study not only demonstrates a new approach to the synthesis of organic zinc compounds, but also provides valuable experience and data to the field of synthetic chemistry. With the continuous development of continuous synthesis technology, we have reason to believe that organic zinc compounds will play a greater role in the future in the fields of drug synthesis and fine chemicals manufacturing.
