b) Cleavage of double bonds (to carboxylic acids, aldehydes or ketones)

A convenient and efficient method for converting cyclohexene into adipic acid has been reported. This protocol represents a new and green viewpoint for the synthesis of adipic acid, since this approach replaces usual hazardous oxidizing agents, such as nitric acid, for an environmentally benign one, aqueous hydrogen peroxide. When a mixture of cyclohexene, hydrogen peroxide, sodium tungstate dihydrate and [CH3(n-C8H17)3N]HSO4 as PTC is kept at 75ºC to 90 ºC for 8 hours, adipic acid is obtained in 93% yield. Adipic acid is an importantchemical, whose production is necessary for the manufacture of nylon-6,6. This procedure is equally applicable to the oxidation of substituted cyclohexenes. Moreover, the oxidation cyclopentene produced crystalline glutaric acid in 90% yield.


 

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The epoxidation of 1,4-bis(allyloxy)butane in the presence of sodium tungstate dihydrate and orthophosphoric acid gives 1-allyloxy-4-glycidoloxybutane and 1,4-bis(glycidoloxy)butane under phase transfer conditions, using 30% hydrogen peroxide as oxidant. Methyltrioctylammonium chloride (Aliquat 336) was used as phase transfer catalyst (PTC). Sodium tungstate dihydrate can be used also as catalyst in the epoxidation of terpenes, such as limonene, geraniol, nerol or 3-carene, using a phosphate buffer solution of H3PO4/NaH2PO4.


 

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2. Applications
Sodium tungstate dihydrate can be used as catalyst or as catalyst precursor in several organic reactions, namely:

a) Epoxidation
The sodium tungstate catalyzed epoxidation of α,β-unsaturated acids by hydrogen peroxide in water has been developed by Payne in 1959, and revisited by Sharpless in 1985, also in water. According to Sheldon, the epoxidation of allyl alcohol to glycidol using hydrogen peroxide and sodium tungstate was applied industrially as an alternative to thetraditional route via epichlorohydrin. The epoxidation procedure developed by Venturello and co-workers, using a Na2WO4.2H2O/H3PO4/quaternary ammonium chloride/aqueous 8% hydrogen peroxide system presents some drawbacks, since requires an excess of olefinic substrates and uses 1,2-dichloroethane, a toxic and carcinogenic chlorinated hydrocarbon solvent. In contrast, Noyori and co-workers reported a clean, halide-free, biphasic epoxidation method with 30% hydrogen peroxide in the presence of sodium tungstate dihydrate, (aminomethyl)phosphonic acid, and a phase transfer catalyst (PTC) such as Q+HSO4- (Q+ =CH3(n-C8H17)3N+) to epoxidize olefins such as cyclooctene (98% yield) or 1-dodecene (87% yield). Functionalized olefins containing an ester, ether, alcohol, or α,β-enone linkage in the same molecule can also be epoxidized by this procedure.


 

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1.Introduction
Sodium tungstate dihydrate is a commercially available reagent which exists in the form of a crystalline white solid. Sodium tungstate dihydrate is usually used in the synthesis of inorganic compounds, namely in polyoxometalates synthesis. It can also be used in organic chemistry as a green catalyst or catalyst precursor, since sodium tungstate dihydrate is able to catalyze the oxidation of several substrates in the presence of hydrogen peroxide, generating only water as the by-product (Scheme 1). On the other hand, the conjugation of this reagent with other inorganic reagents used in polyoxometalates synthesis permits the formation of several complexes, mainly peroxocomplexes, which can catalyze some oxidation reactions by themselves.


 

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Tungsten carbide v-shaped bits are referred to the bits that made of tungsten carbide and typically used for signs and V-carving. Generally, there are two factors,which are likely to affect the profile of the v-bits, angle and diameter.

Angle

It is commonly referred to the included angle. The most well accept angle of v-bits are 30°, 45°,60°, 90°, and 120°. The relevant tip of a V-bit presents as a true point, a small radius or a flat.

Diameter

It is the width of a full depth cut at the surface of the workpiece, measured perpendicular to the shank.


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Tungsten acid can be used for co-solvents.

A second solvent added in small quantities to enhance the solvent power of the primary solvent.

Common co-solvents have two categories: one is certain organic acids and sodium salts, such as sodium benzoate, sodium salicylate, p-amino benzoic acid; the other is amides, such as urea , nicotinamide, acetamide. The solubilization mechanism is complex, many of the which is still unclear, therefore, there is no clear rules to follow on the selection of co-solvent, generally choose the substances that can obtain water-soluble molecular complexes rehabilitation salt or association complex according to the nature of drugs.

 

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Tungsten acid can be used for waterproofing material.

Water-proof or water-resistant describes objects relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environments or under water to specified depths. Waterproofing describes making an object waterproof or water-resistant (such as a camera, watch or mobile phone).

"Water resistant" and "waterproof" often refer to penetration of water in its liquid state and possibly under pressure, whereas damp proof refers to resistance to humidity or dampness. Permeation of water vapor through a material or structure is reported as a water vapor transmission rate.

The hulls of boats and ships were once waterproofed by applying tar or pitch. Modern items may be waterproofed by applying water-repellent coatings or by sealing seams with gaskets or o-rings.

Waterproofing is used in reference to building structures (basements, decks, wet areas, etc.), watercraft, canvas, clothing (raincoat, waders) and paper (e.g., milk and juice cartons).


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Tungsten carbide fluted countersink cutter is a cone-shaped tool made of tungsten carbide with one or several flutes along the cutting edge. This type countersink cutter is very often required to work with countersunk-head screw for seating preparation or pre-machining for tapping.

In practice, the most well accepted angels of this countersink cutter comprise 60°,  82°,  90°,  100°, 110°and 120°, among which the most common two are  82°and  90°as the countersunk-head screws very often have an 82°or 90°angle. Specially, the typical angle of countersunk fasteners is 100° in the aerospace industry.

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During framing operation, tungsten carbide miter saw could cut through a workpiece in a quick and controlled motion by spinning down circular saw blade, and the tungsten carbide tipped teeth enable it to deal with hard material. The workpiece is typically held against a fence to form a cutting angle (angle between the blade plane and the longest workpiece edge), which will be fixed at 90°in standard position.
 

Miter index, as one primary characteristic of tungsten carbide miter saw, it enables the blade angle changes to be matched with the fence. For most miter saws miter index could be set as precise one-degree incremental changes.


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Tungsten carbide miter saw is referred to a saw with teeth made of tungsten carbide that could create desired crosscuts and miters in machining operation.

In general, there are two common types of miter saw, which are manual miter saw and power miter saw. Manual miter saw is basic manual saw with the help of miter box and depended from rollers or slides in a metal guide to make accurate crosscuts and miters. They are occasionally used in picture framing and manual woodworking processes. For the power miter saw, it is a portable and relatively small saw, which is able to make a crosscut with accuracy and timeliness via a selected angle. The common applications comprise framing and molding cutting, and its blade sizes vary from eight to twelve inches.   


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