Weighing tubes, micro

Principle. This is essentially a small-scale modification of the macro piethod described on p. 416, the substance being completely oxidised in a sealed tube with fuming nitric acid in the presence of silver nitrate, the halogen being thus converted into silver halide. The collection and weighing of the silver halide require special techniques on the semi-micro scale. 

Resin 4 (R1 = CH3) (50 mg, 0.014 mmol) was weighed into a conical Personal Chemistry Smith process vial equipped with a conical-shaped stir bar. To the resin was added 4-fluorophenylboronic acid (11 mg, 0.08 mmol), DMF (1 ml), 2 M aqueous sodium carbonate (80 pi), and di-chlorobis(triphenylphosphine)palladium(II) (1-2 mg). The heavy walled glass vial was crimp sealed and placed on the Gilson platform. The micro-wave program was set to a 5 min duration at 180° on the normal absorption setting and the vial was then processed. After completion, the vial was decrimped and resin 5 (R1 — CH3, R2 = 4-F-phenyl) was transferred to a fritted tube and washed with DMF, H20, MeOH, and DCM (3x each). 

The apparatus consists of a reaction flask (A), a condenser-scrubber trap (B), a series of traps (C) and a micro weighing bottle (D). The reaction flask in A is a round-bottomed flask having a volume of approximately 13 ml fitted with a gas inlet tube in the form of a capillary tube extending to the bottom of the flask. The scrubber trap in B has a side arm with a ground glass stopper in the upper part and is capable of holding a maximum of about 4 ml of wash solution. 

Support a small clean test-tube (e.g., 75 x 10 mm.) in a hole bored in a cork so that it will stand conveniently on the pan of a balance. Weigh the tube. Introduce about 60 mg. of the compound of which the molecular weight is to be determined, and weigh again. Then add 600-600 mg. of pm-e, resublimed camphor (c.g., the micro-analytical reagent,... 

When administering an enema, it is almost impossible to transfer all liquid to the rectum. A small amount will always remain in the bottle or giving tube. Small enema bottles are therefore filled with an excess of liquid. The required excess depends on the model of the micro-enema bottle and on the physical properties of the micro-enema liquid, in particular the viscosity. The residual volume, and thus the required excess, can be determined by weighing a bottle, filling it and emptying it by squeezing, after which it is reweighed. 

Evaporate the combined extracts on a water-bath under a jet of air to about 3 ml, completely transfer the residue with small portions of chloroform to a tared 50-ml beaker, and heat again to evaporate the solvent completely. Heat further at 105° for thirty minutes, cool in a desiccator and weigh the residue of triacetyl adrenaline. Add 5 0 ml of chloroform, cover the beaker, gently swirl until the residue is completely dissolved, and detennine the specific rotation, Ry using a 2-dm, semi-micro polarimeter tube. 

Procedure A micro test tube fitted with a rubber stopper is filled with 0.3 g of p-chloroaniline, 0.6 ml of benzoyl chloride, and 0.9 ml of pyridine, and the mixture is heated at 80 °C in a water bath for 20 min. After the immersion of the tube into the water bath the rubber stopper is taken off very briefly (to diminish the pressure in the tube). The solvent is then evaporated to dryness on a boiling water bath (the vapors are sucked off with a water pump) and the residue is mixed with 1 ml of 10% HCl. When the mixture is settled the supernatant is eliminated with a micropipette and the residue is washed with 0.5 ml of water in the same manner. The washing is continued with two portions (0.5 ml each) of 10% sodium carbonate solution and two 0.5 ml portions of water. The residue is filtered off using a filtration tube and is washed with 0.5 ml of water. Yield, 0.48 g mp (unsharp), from 45 °C. For crystallization the product is dissolved in 13 ml of boiling ethanol and the solution is diluted with water to incipient turbidity (1 ml). This is dissolved by heating again, and the solution is allowed to cool slowly. The crystals that formed weighed 0.33 g, mp 102 — 103 °C. After a second crystallization from 10 ml of methanol and 2 ml of water the yield was 0.20 g, mp 104 °C. 

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