Rubber dam

A rubber dam is fitted over the top of the Buchner funnel and held in place by rubber bands in order to remove as much of the water as possible. 

In a 3-I. round-bottomed flask 250 g. of commercial calcium hypochlorite is dissolved in i 1. of warm water and a warm solution of 175 g. of potassium carbonate and 50 g. of potassium hydroxide in 500 cc. of water is added. The flask is stoppered and shaken vigorously until the semi-solid gel which first forms become quite fluid. The suspended solid is removed by filtration on a large Buchner funnel, washed with 200 cc. of water, and sucked as dry as possible with the aid of a rubber dam and an efficient suction pump. The filtrate of approximately 1500 cc. is placed in a 3-I. round-bottomed flask and is ready for the addition of methyl /3-naphthyl ketone. 

Since the mixture filters rather slowly, even after storage overnight, a Buchner funnel of at least 20 cm. diameter should be used, and a hard grade of filter paper (such as Whatman no. 50) is recommended. Use of a rubber dam helps to express solvent and exclude moisture from the hygroscopic product. 

Radial rubber dams that separate between the feed, wash stages, cake discharge and cloth wash, and cloth drying zones to prevent the mixing of filtrates. 

Exposure of this salt to the atmosphere causes discoloration that may persist in the final product. A slight discoloration at this stage does not appear to affect the quality of the final product. A rubber dam is helpful on days of high humidity. 

The precipitate is collected on filter paper (Note 7) in a Buchner funnel by vacuum filtration and is washed with 100 ml. of absolute ethanol. The solid is slurried in three 75-ml. portions of distilled water (Note 8), 100 ml. of absolute ethanol, two 100-ml. portions of reagent-grade acetone, and two 100-ml. portions of anhydrous ethyl ether. The filter cake is pressed dry in the funnel with suction by means of a piece of rubber dam, transferred to a tared, 500-ml., round-bottomed flask, and dried under reduced pressure (0.01 mm.) at room temperature for 24 hours (Note 9). The weight of the dry silver salt of succinimide is 51-54 g. (88-94%). 

A rubber dam was fastened tightly over the top of the Buchner funnel by means of rubber bands. It was pulled down onto the surface of the filter cake by the vacuum. 

C. (+)- and (-)-a-(Isopropylideneaminooxy) propionic acid-(-)-ephedrine salts. A solution of 36.6 g. (0.200 mole) of (— )-ephedrine monohydrate (Note 7) in 800 ml. of ethyl acetate containing 6% of ethanol (Note 8) is placed in a 2-1. beaker, d,l-a-(Isopropylideneaminooxy)propionic acid (29.0 g., 0.200 mole) is dissolved in this solution by stirring (Note 9). The beaker is covered securely with a rubber dam, cooled for a short period in an ice bath, placed in a refrigerator at 0-5°, and allowed to remain undisturbed for 8-16 hours after crystallization has begun (Note 10). The solid mass of crystals is filtered by suction, and the funnel is covered with a rubber dam to remove most of the solvent. The solid product is placed in a 500-ml. beaker, 250 ml. of ethyl acetate is added (Note 11), and the mixture is heated until all the solid has dissolved. The solution is cooled, placed in a refrigerator for several hours, and filtered the crystalline precipitate is dried in air. The yield of the (—)-ephedrine-(+)-a-(isopropylideneaminooxy)propionic acid salt is 22-25 g. (71-81%) m.p. 115-119° (Notes 12 and 13) [ ]2°d -4.2° (c 1.5, chloroform). 

Leave the aspirator on and let air pass through the crystals to help them dry. You can put a thin rubber sheet, a rubber dam, over the funnel. The vacuum pulls it in and the crystals are pressed clean and dry. And you won t have air or moisture blowing through, and possibly decomposing, your product. Rubber dams are neat. 

Pine oleoresin [1 kg. containing 260 g. (0.86 mole) of levo-pimaric acid] (Notes 1 and 2) is dissolved in 2 1. of acetone in a 4-1. beaker. A solution of 200 g. (2.2 moles) of 2-amino-2-methyl-1-propanol (Note 3) in 200 ml. of acetone is added as rapidly as possible with stirring. The pasty precipitate which forms almost immediately is collected by suction filtration and is pressed as dry as possible using a rubber dam (Note 4). The crude moist precipitate is returned to a 2-1. beaker and is dissolved in the minimum volume ( 1 1.) of boiling methanol. The methanolic solution is cooled to 5° in a refrigerator and stirred occasionally to expedite crystallization. When the crystallization is completed, the solid is collected by suction filtration. The precipitate is redissolved in a minimum volume of boiling methanol ( l 1.) (Note 5), the solution concentrated to two-thirds its original volume (Note 6), cooled to 5°, and the amine salt allowed to... 

The use of a rubber dam is essential in this step to effect the separation of the residual acetone. It is also beneficial to use a rubber dam in the other suction filtrations in this process. 

B. Ethyl l,3-dihydroxy-2-naphthoate. In a 1-1. flask 1 volume (87 ml.) of the crude ester is added in one lot to 3 volumes (261 ml.) of concentrated sulfuric acid without cooling, and the solution is allowed to stand for about 1 week (Note 4). The whole mixture, including any precipitate which may have formed, is poured slowly with stirring into a mixture of 1 kg. of icc and 500 ml. of water (Note 5) the solid yellow ester is filtered with suction, washed with a small amount of cold water, pressed in the filter for 30 minutes with a rubber dam, and finally dried in a vacuum desiccator. The yield of ester melting at 80° is 58-68 g. (50-59%, based on the malonic ester used). 

The solution is chilled overnight in an ice chest, and the precipitated yellow crystals are collected on a 19-cm. Buchner funnel. The crystals are washed with 270 ml. of ice-cold water and pressed as dry as possible with a rubber dam. The filter cake can be dried (Note 3) in air or in a vacuum desiccator over calcium chloride and soda lime. The yield of 2-nitro-4-methoxyacetani-lide melting at 116-116.5° is 158-168 g. (75-79%). 

B. 2-Nitro-4-metfwxyaniline. A mixture of 160 g. of 2-nitro-4-methoxyacetanilide and 250 ml. of cold Claisen s alkali (Note 4) in a 2-1. beaker is stirred and warmed on a steam bath for 15 minutes it first becomes liquid and then sets to a thick, red paste. After the addition of 250 ml. of hot water the mixture is stirred and digested on a steam bath for an additional 15 minutes and then cooled to 0-5°. The product is collected on a 19-cm. Buchner funnel, washed with three 160-ml. portions of ice-cold water, and pressed as dry as possible with a rubber dam. The yield of vacuum-dried product melting at 122.5-123° is 122-4 g. (95-97%). 

Removal of all of the hydrobromic acid by washing is critical to the success of the next reaction. If the filtrate is not basic after washing with cold 10% aqueous ammonium hydroxide the washing should be continued until the filtrate is basic. Disconnection of the vacuum during each washing is recommended. The final aqueous wash should be no more basic than pH 8-9. Use of a rubber dam facilitates the filtration and washing. 

To a solution of 39.4 g of ethyl 3- and 4-(4-chloro-l-oxobutyl)-a,a-dimethylphenylacetate dissolved in 800 mL of methanol and 200 mL of water was added 40 g of NaOH. The mixture was refluxed for one hour. The cooled mixture was then concentrated in vacuo. The concentrate was diluted with water and washed with 2 portions of EtOAc. The aqueous layer was acidified with concentrated HCI and extracted with 2 portions of EtOAc. The extracts were dried over MgS04, filtered, and concentrated in vacuo to afford 30.3 g of crude product. The crude product was dissolved in 600 mL of EtOAc, 38 g of cinchonidine was added, and the mixture was stirred overnight. The resulting solids were filtered and washed with EtOAc and sucked dry under a rubber dam to afford 25 g of a solid 4-(cyclopropyl-oxo-methyl)-a,a-dimethylphenylacetic acid. 

Repeat Animal Patch (RAP) test - compares irritation potential of surfactants. Solutions were applied to the clipped back of immobilized albino mice with a saturated cotton-tipped applicator. The test site was covered with a rubber dam to prevent evaporation. This process was repeated seven times at intervals of 10 min. The skins were evaluated microscopically for epidermal erosion. 

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