Bonded Phases - The Large Scale Preparation of Bonded Phases
The Large Scale Preparation of Bonded Phases
The method used for preparing bonded phases on a larger scale is essentially the same as that just described, but with some minor modifications to reduce toxic hazards and render the process more amenable to large scale operation. If chlorsilane reagents are used, the reaction is normally carried out in an appropriately large flask fitted with a reflux condenser and a water scrubber. A diagram of a suitable apparatus for synthesizing up to a kilo of material is shown in figure 2.
Figure 2. Apparatus for the Preparation of Bonded Phases
The same proportion of starting materials can be used on the macro scale as was used in the laboratory scale but, in order to reduce toxicity exposure on the larger scale, pyridine is not used to to scavenge the hydrochloric acid that is evolved. The hydrochloric acid gas passes out of the condenser, then through a scrubber down which water is passing to remove the acid. By this means, the acid is removed as a very dilute solution to waste. It can be an advantage to arrange for a stream of nitrogen to be passed through the reaction mixture to aid in removing the hydrochloric acid. Apart from the modifications described and the use of larger vessels and filters, the procedure is precisely the same as that described for the laboratory scale synthesis. However, in the large-scale preparation of bonded phases, the alkoxy reagents are far simpler to use as they involve no hydrochloric acid gas disposal and the operation is generally easier to carry out. The preparation of several kilos of bonded phase is quite practical, providing that equipment of sufficient size is available. In general, increasing the scale of synthesis should not significantly affect the quality of the material produced.
The above synthetic methods are satisfactory for most types of bonded phases and in particular the hydrocarbon or reverse phases. However. if the bonded group contains unique functional groups, a slight modification of the above procedure may be necessary.