Project: Formation of Grignard-reagent

Lab exp no: - CPA-exp no: 1002-14 Date: 021022
Issued by Roland Ohlsson File: 100214.xls

Stainless steel reactor with propeller stirrer was used. Diethylene glycol / water (60/40 wt%) in the ref.bath.
To the reactor 3,0 g flakes of Magnesium and 110 ml of Tetrahydrofuran (THF) was charged. The temperature was set to -8°C and when steady-state was
reached 52,8 g of substrate-solution (18,7 g of solid substrate dissolved in 34,1 THF) was added via a peristaltic pump over a period of 110 minutes.
During the addition the pump was stopped twice to check for eventual accumulation of energy. After concluded addition the batch was left for post-reaction
for approximately 90 minutes.

Results

Cp (Mg) = 1,0 J/g*K Cp (THF) = 1,72 J/g*K Cp (substrate) = ca 2 J/g*K

m(Mg) 3,00 g m(Mg+THF) 100,9 g Enthalpy 371,0 kJ/mole
n(Mg) 0,12 mole mCp(Mg+THF) 171,4 J/K Acc 2 9,9 %
m(substrate) 18,70 g m(sub-sol) 52,8 g DTad(max) 14,0 °C
n(substrate) 0,10 mole mCp(sub-sol) 96,1 J/K DTad(max, theo) 140,0 °C

Reaction enthalpy was calculated by numeric integration of the reaction power output over time. The degree of accumulation was calculated by the comparison of the added amount of substrate and corresponding enthalpy build up for each time segment (5 sek).

A well known problem concerning the formation of the Grignard compound is the induction period before the reaction starts. An induction period might leed to dangerous situations if unreacted material is accumulated. The reacting properties of the current batch of chemicals used are easely determined as well as the necessary need for cooling in full scale operation.

The CPA202 gives the result from the reaction direct on-line. The universal calibration of the reactor means that the system directly presents the True Heat Flow and the Total Power from the reaction independent of the wetted jacket area or the heat transfer properties.