Brown hydrogenation

Computer representation of methane and ethane molecules inside one of the hexagonal pores of MCM-41. Red = oxygen blue = silicon light blue = hydrogen brown = carbon. 

Varga A complex process for hydrogenating brown coal and high molecular weight asphaltenes. The process uses hydrogen at a high pressure, in the presence of an iron oxide catalyst. Invented by J. Varga in Budapest... 

Hydrogen must be considered as a member of Group I in such cases as — CHO the hydrogen must be ignored and only the remaining element considered. See also Crum Brown s rule. 

Crude oils appear as liquids of varying viscosities. Their color can range from green (crude from Moonie, Australia) to dark brown (crude from Ghawar, Saudi Arabia). They can have an odor of hydrogen sulfide, turpentine or simply hydrocarbon. 

Cruzan J D, Braly L B, Liu K, Brown M G, Loeser J G and Saykally R J 1996 Quantifying hydrogen bond oooperatively in water VRT speotrosoopy of the water tetramer Science 271 59-62... 

In presence of hydrochloric acid, tin(II) in aqueous solution (1) is precipitated by hydrogen sulphide as brown SnS, and (2) will reduce mercury(II) chloride first to mercury(I) chloride (white precipitate) and then to metallic mercury. 

When hydrogen sulphide is bubbled into an acidic solution of an antimony or a bismuth salt an orange precipitate, SbjSs, or a brown precipitate, BijS, is obtained. Bismuth(III) sulphide, unlike antimony(IIl) sulphide, is insoluble in lithium hydroxide. 

Manganese(IV) oxide is a dark-brown solid, insoluble in water and dilute acids. Its catalytic decomposition of potassium chlor-ate(V) and hydrogen peroxide has already been mentioned. It dissolves slowly in alkalis to form manganates(lW), but the constitution of these is uncertain. It dissolves in ice-cold concentrated hydrochloric acid forming the complex octahedral hexachloromangan-ate(IV) ion ... 

For a cobalt(ll) salt, the precipitation of the blue->pitik cobalt(II) hydroxide by alkali, or precipitation of black cobalt(II) sulphide by hydrogen sulphide provide useful tests the hydroxide is soluble in excess alkali and is oxidised by air to the brown CoO(OH) . 

Copper(II) ions in aqueous solution are readily obtained from any copper-containing material. The reactions with (a) alkali (p. 430), (b) concentrated ammonia (p 413) and (c) hydrogen sulphide (p. 413) provide satisfactory tests for aqueous copper(II) ions. A further test is to add a hexacyanoferrate(II) (usually as the potassium salt) when a chocolate-brown precipitate of copper(II) hexacyanoferrate(II) is obtained ... 

Cadmium is a soft metal, which forms a protective coating in air, and burns only on strong heating to give the brown oxide CdO. It dissolves in acids with evolution of hydrogen ... 

Sulphur. Moisten the centre of a filter-paper with lead acetate solution. Then add about 10 ml. of dilute hydrochloric acid to the residue in the evaporating-basin, and at once cover the latter with the paper. If zinc sulphide is present in the residue, the hydrogen sulphide evolved will give a definite daA brown coloration with the lead acetate paper. The presence of hydrogen sulphide can often be confirmed by its odour. 

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

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