Amber heat treated

Empire 1.2S Heat-treated green Baltic amber cabochon. 

Figure 1.32 Old pressed amber beads (Victorian), and heat-treated Baltic amber beads (modern).

Discoidal stress fi actures ( sun spangles ) in natural amber that has been heat treated are uneven and have lines radiating firom the centre of each spangle (Figs 1.21 and 1.22). Viewed side-on they become almost invisible. Artificial sun spangles in plastic tend to be even in shape and when viewed side-on they remain obvious (Figs 1.23 and 1.24). 

A solution of 9.4 g 4,5-dimethoxy-2-ethoxy-l-allylbenzene in 10 mL EtOH was treated with 20 g flaked KOH, and heated on the steam bath. The progress of the isomerization was followed by the assay of isolates by GC. After 5 h, the reaction mixture was poured into 250 mL H20 which immediately generated a pasty solid. This was sucked free of solvent and other liquids on a sintered funnel, giving 5.5 g of trans-4,5-dimethoxy-2-ethoxy-l-propenylbenzene as an amber solid with a mp of 65-67 °C. A small analytical sample from hexane had a mp of 68 °C. 

A suspension of 4 g of trans-2-(2,5-dimethoxy-4-methylphenyl)-cyclopropanecarboxylic acid in an equal volume of H20, was treated with sufficient acetone to effect complete solution. This was cooled to 0 °C and there was added, first, 2.0 g triethylamine in 35 mL acetone, followed by the slow addition of 2.5 g ethyl chloroformate in 10 mL acetone. This was stirred for 0.5 h, and then there was added a solution of 1.7 g NaN i in 6 mL If20, dropwise. After 1 h stirring at 0 °C, the mixture was quenched by pouring into H20 at 0 °C. The separated oil was extracted with EtzO, and extracts dried with anhydrous MgS04. Removal of the solvent under vacuum gave a residue of the azide, which was dissolved in 10 mL anhydrous toluene. This solution was heated on the steam bath until the nitrogen evolution was complete, and the removal of the solvent under vacuum gave a residue of crude isocyanate as an amber oil. This intermediate isocyanate was... 

Ultraviolet lig t. Most amber and copal fluoresces in UV lig t (Figs 1.13 and 1.16). This fluorescence dims if the amber has been treated with heat to clarify it or to press it. It also tends to dim and change colour with age - fleshly cut or polished amber will alwa3rs fluoresce more strongly. 

A solution of 17 g of 4-methoxy-2-(2-methylallyl)phenol in 56 g acetic acid was treated with 8.4 g zinc chloride followed with 28 mL concentrated HCI. This mixture was heated at reflux temperature with a mantle for 1 h. After cooling, this was poured into H20 and extracted with 2x150 mL CH2CI2. The pooled extracts were washed with several portions of 8% NaOH, until the extracts were colorless. The organic fraction was then washed with H20, and the solvent removed to yield 5.8 g of 2,2-dimethyl-5-methoxy-2,3-dihydrobenzofuran as a pale amber oil with a pungent smell. This was purified by distillation, giving a fraction of an off-white oil with a bp of 136-138 °C at 33 mm/Hg. 

---