Tollens reaction

Condensation of carbonyl compounds possessing an a-hydrogen with formaldehyde in the presence of base. 

Godleski, S. A. In Comprehensive Organic Synthesis Trost, B. M. Fleming, I., eds. Vol. 4. Chapter 3.3, Pergamon Oxford, 1991. (Review). 

Moreno-Manas, M. Pleixats, R. In Advances in Heterocyclic Chemistry Katritzky, A. R., ed. Academic Press San Diego, 1996,66,73. (Review). 

---

Although the Tollens reaction is a useful test for reducing sugars, it doesn t give good yields of aldonic acid products because the alkaline conditions cause decomposition of the carbohydrate. For preparative purposes, a buffered solution of aqueous Br2 is a better oxidant. The reaction is specific for aldoses ketoses are not oxidized by aqueous Br2. 

When aliphatic nitro compounds are used instead of aldehydes or ketones, no reduction occurs, and the reaction is essentially a Knoevenagel reaction, though it is usually also called a Tollens reaction ... 

Li et al. reported first on the decoration of hydrothermal carbon spheres obtained from glucose with noble metal nanoparticles [19]. They used the reactivity of as-prepared carbon microspheres to load silver and palladium nanoparticles onto then-surfaces, both via surface binding and room-temperature surface reduction. Furthermore, it was also demonstrated that these carbon spheres can encapsulate nanoparticles in their cores with retention of the surface functional groups. Nanoparticles of gold and silver could be encapsulated deep in the carbon by in situ hydrothermal reduction of noble-metal ions with glucose (the Tollens reaction), or by using silver nanoparticles as nuclei for subsequent formation of carbon spheres. Some TEM images of such hybrid materials are shown in Fig. 7.4. 

In Tollens reaction an aldehyde or ketone containing an a hydrogen is treated with formaldehyde in the presence of Ca(OH)2 or a similar base. The first step is a mixed aldol reaction (6-39). 

B). Lignin contains carbonyl groups in various positions of the side chain. Hydroxymethyl groups can be introduced into the neighboring positions by substituting their activated hydrogen atoms (Tollens reaction). 

To find the best conditions for Tollens reaction, several model compounds were used containing CO groups in a- or /3-side chain positions. 

Optimum conditions (Table VI) for ring-hydroxymethylation of 1 mole phenol 2 moles of CH20, 1 mole of NaOH, 0.8-1 NaOH concentration, 3 to 4 days at room temperature for Tollens reaction (1 mole of model ketone) 8 moles of CH20, 2 moles of NaOH, 2N NaOH concentration, 5 days at room temperature. 

Figure 19.2 Self-similarity analysis for nanotextured silver surfaces prepared in different ways. The root mean square roughness inferred from atomic force microscopy is plotted versus measurement area. The various surfaces are 100 nm thick evaporated silver films (solid squares, red line)-, 5.2 nm thick evaporated silver films (open circles, green line) nanoparticle films assembled from colloid attachment to self-assembled monolayers (solid circles, blue line) films from deliberate precipitation of silver colloid (solid up-triangles, black line) Tollens reaction films (open down-triangles, orange line). Lines with slopes H = 1.0 and H = l.S representing two-dimensional and 1.5 dimensional surfaces respectively are...

For reasons clear from the introduction, enhancement of phosphorescence is a particularly attractive application of plasmonics to OLED technology. Since carriers are injected into an OLED from separate contracts, their spins are uncorrelated and spin statistics dictate preferential formation of triplet excited states. Since these are generally poor emitters at ambient temperature, metallic enhancement of the phosphorescent rate would be desirable. Moreover, triplet states are typically long-lived and prone to oxidation reactions so that reduction of the triplet lifetime could potentially improve stability of the phosphors. PtOEP is a model phosphor and its application to electroluminescence was pioneered by the groups of Forrest and Thomson (46-47). We have investigated plasmonic enhancement of the PtOEP phosphorescence on silver surfaces prepared using the Tollens reaction. Dilute PtOEP in a polymer binder was spin cast onto substrates with various densities of nanotextured silver and assumed to deposit conformally, the spin speed being used to control the approximate thickness of the overlayer. 

When aliphatic nitro compounds are used instead of aldehydes or ketones, no reduction occurs, and the reaction has been referred to as a Tollens reaction (see 16-43). However, the classical condensation of an aliphatic nitro compound with an aldehyde or ketone is usually called the Henry reaction or the Kamlet reaction, and is essentially a nitro aldol reaction. A variety of conditions have been reported, including the use of a silica catalyst, Mg—A1 hydrotalcite, a tetraalkylam-monium hydroxide,proazaphosphatranes, " or an ionic liquid.A solvent free Henry reaction was reported in which a nitroalkane and an aldehyde were reacted on KOH powder. Potassium phosphate has been used with nitromethane and aryl aldehydes. The Henry reaction has been done using ZnEt2 and 20%... 

---