Reduction methods

1 Reduction Methods. Early methods used a zinc-hydrochloric acid reduction (Gutzeit method), together with some kind of collecting device for the hydrides formed  

M is the analyte and m may be equal to n or not (for example, As and As are both reduced to AsHs). Hydrides were collected in U-tubes in a nitrogen trap or in rubber balloons. Titanium(iii) chloride—hydrochloric acid and magnesium-zinc reductants were used to extend the hydride method to bismuth, antimony, and tellurium. For some elements, especially tin, lead, and tellurium, the hydride formation reaction is relatively slow and hence the collection vessel is necessary. In addition, arsenic(v) must be reduced to arsenic(iii) by tin(ii) chloride or potassium iodide before the actual hydride generation when a metal-acid reduction is employed. 

Sodium borotetrahydride is now generally used as the reductant in various hydride generation methods. The reduction may be illustrated by the following reactions  

The hydride is generated by first adding the sample to a HCl solution (0.5-5.0 moll ) and then NaBH4 (about 1% solution). The hydride formation by NaBH4 is very fast and the hydride vapour may be flushed immediately or after reaction times of 10 to 100 seconds into a silica tube atom cell at carrier gas flow rates of 20 to 100 mls.  

Advantages of sodium borotetrahydride as the reductant are (i) The reaction time is fast (varies from 10 to 30 seconds) (ii) NaBH4 can be 

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Cardona, A. and Idelsohn, S., 1986. Solution of non-linear thermal transient problems by a reduction method. Int. J. Numer. Methods Eng. 23, 1023-1042. 

When Strike wrote the first edition Strike considered there to be only one, decent reduction method for the p-Nitropropene. But since then Strike has come across quite a few new ways that make this conversion very, very easy and varied. A lot of the ways were conjured up by one, industrious lab from Tennessee. We ll get to those in a minute. But first let s start off with the basic, default recipe for the reduction of p-Nitropropenes. 

Although Strike found most of these articles on Strike s own, our good friend and learned scholar Osmium emailed Strike some of the above group s articles and quite a few more that we will get at in just a bit. The following methods can be read about in the original articles in which they were published [49-51]. But there is a nice review by the same authors in which a representative example of each of their methods is included [52]. The following were taken from that review. X and speed chemists just substitute an equimolar amount of their respective p-Nitropropene for the one in the methods below. Also, it should be obvious that these reduction methods will work just fine on 2CB and other phenethylamine intermediates. 

METHOD 5 Contributed by Osmium [53], The paper reads (at least to Strike) that this reduction method can work to reduce the formyl intermediate made in the Leuckart reaction directly into MDMA instead of needing to hydrolyze to MDA with HCi (don t ask). For this reaction one substitutes an equimolar amount of p-Nitropropene for the 3,4-dimethoxybenzylcyanide in the representative experimental below ... 

With Phenylpropanolamine at hand (or ephedrine and pseudo-ephedrine) one would next need to reduce that alpha carbon OH group to get the final amine. Strike understands that the current favorite methods for doing this involve lithium and amine. HI and red P or other iodine related protocols. So when you meth heads ruin every aspect of those methods as well, what will you do then The following are a couple of OH reduction methods (Strike thinks) that have applicable use [99-100]. 

The only other thing Strike has to say is that some have hinted that all of those p-nitropropene reduction methods (or at least... 

The same reduction methods may be applied to the conversion of nitriles to pn mary amines... 

The methylene blue and resazurin reduction methods indirectly measure bacterial densities in milk and cream in terms of the time interval required, after starting incubation, for a dye—milk mixture to change color (methylene blue, from blue to white resazurin, from blue through purple and mauve to... 

Hydroisoquinolines. In addition to the ring-closure reactions previously cited, a variety of reduction methods are available for the synthesis of these important ring systems. Lithium aluminum hydride or sodium in Hquid ammonia convert isoquinoline to 1,2-dihydroisoquinoline (175). Further reduction of this intermediate or reduction of isoquinoline with tin and hydrochloric acid, sodium and alcohol, or catalyticaHy using platinum produces... 

The introduction of tritium into molecules is most commonly achieved by reductive methods, including catalytic reduction by tritium gas, PH2], of olefins, catalytic reductive replacement of halogen (Cl, Br, or I) by H2, and metal pH] hydride reduction of carbonyl compounds, eg, ketones (qv) and some esters, to tritium-labeled alcohols (5). The use of tritium-labeled building blocks, eg, pH] methyl iodide and pH]-acetic anhydride, is an alternative route to the preparation of high specific activity, tritium-labeled compounds. The use of these techniques for the synthesis of radiolabeled receptor ligands, ie, dmgs and dmg analogues, has been described ia detail ia the Hterature (6,7). 

Berlin Institute Method. This method is for determination of invert sugar in products containing not more than 10% invert in the presence of sucrose. It is a copper reduction method that utilizes MbUer s solution, which contains sodium carbonate. 

Knight and Allen. This is a copper reduction method for reducing sugars in white sugar up to 0.02%. It utilizes EDTA to determine excess unreacted copper. Tests undertaken in 1994 to extend the range of this method were unsuccesshil. In spite of poor performance in ring tests, it remains an official ICUMSA method. 

Tabic 13. Slab-Zinc Production in the United States by Various Reduction Methods, 10001... 

Table 2. Curve Equations and Linear Reduction Methods...

Dialkylation of an amine or sulfonamide with a 1,3-dihalide provides a further route to azetidines <79CRV33l, 64HC( 19-2)88 5). Examples of this approach are the formation of N-tosylazetidine from tosylamide and l-bromo-3-chloropropane and the formation of N-alkylazetidinyl esters (36). The latter reaction works well except for R=Me the former provides a useful route to azetidine since the tosyl group can be removed by reductive methods. 

The number of speed reduetions is another way to classify conveyor drives. Most common of the speed-reduction methods is the two-step system, in which the motor is coupled to a speed reducer and the slow-speed shaft of the reducer is connected to the conveyor-drive shaft by a V belt or a roller chain. The second reduction not only permits the use of a simpler speed reducer but also allows a more flexible layout of the motor and reducer mounting plate. On many installations this eliminates the need for a specially designed drive mount. 

Phosphorus and Silicon in Waters, Effluents and Sludges [e.g. Phosphorus in Waters, Effluents and Sludges by Spectrophotometry-phosphomolybdenum blue method. Phosphorus in Waters and Acidic Digests by Spectrophotometry-phosphovanadomolybdate method. Ion Chromatographic Methods for the Determination of Phosphorus Compound, Pretreatment Methods for Phosphorus Determinations, Determination of silicon by Spectrophotometric Determination of Molybdate Reactive Silicon-1 -amino-2-naphthol-4, sulphonic acid (ANSA) or Metol reduction methods or ascorbic acid reduction method. Pretreatment Methods to Convert Other Eorms of Silicon to Soluble Molybdate Reactive Silicon, Determination of Phosphorus and Silicon Emission Spectrophotometry], 1992... 

Gradual velocity reduction method. This method is a variation of the constant friction approach, where a maximum velocity is used for the main and branch ducts. This procedure provides a reasonable solution and choice between the velocity, diameter, and resistance. The method is not useful to provide the same static pressure at each outlet. 

It should be noted that this reductive method compliments other reactions for the preparation of certain thermodynamically more stable labeled epimeric alcohols (see section III-B). 

DDQ, CH2CI2, 58°, 2 days, 52% yield. In this example, conventional reductive methods failed. Anhydrous DDQ was used to prevent acid-promoted decomposition. 

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