With the aqueous gold chloride reagent, two forms of crystals are observed for 4-MeOPP and their formation is concentration dependent. Clusters of thick irregular tablets are formed at the edge of the drop. These are colorless in bright field and bright yellow under crossed polars. The other form of crystals observed are long red rods that are arranged either individually or in loose clusters. A composite of these forms may also be observed.
Orange crosses similar to the ones observed with the acidic gold chloride reagent may also be observed at high concentrations when the reaction occurs very quickly.
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