Microwave Mediated synthesis of cyclic compounds
- Authors: Ndebvu, Rumbidzayi
- Date: 2011
- Subjects: Cyclic compounds -- Synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:18488 , http://hdl.handle.net/11260/d1007382
- Description: The scope of microwave induced synthesis of various cyclic compounds was investigated and considerably expanded. The advantages of this synthetic method were clearly demonstrated when compared to conventional heating methods of organic synthesis. The exposure of organic compounds to continual Ultraviolet (UV) radiation damages the materials and reduces their chemical and physical properties and in most cases irreversibly and this is not only a concern for industry but for consumers as well. Particularly prevalent are incidences of skin cancer now linked to UV radiation. Research efforts are directed towards finding cheap and efficient UV-absorbers to protect such light sensitive materials. Phenyl salicylates and hydroxybenzophenones constitute families of UV-absorber compounds, and this has necessitated this research. The condensation of differently substituted phenols with salicylic acid, catalyzed by either phosphoric acid (PPA), POCl3/ZnCl2 or ZnCl2 afforded the anticipated phenolic type UV -absorber molecules such as phenyl salicylate, 4-hydroxyphenyl-2-hydroxybenzoate, 2,3-dihydroxyphenyl-2-hydroxyphenylbenzoate, 3-hydroxyphenyl-2-hydroxybenzoate, (2,4-dihydroxyphenyl)(2-hydroxyphenyl)methanone, (2,3-dihydroxyphenyl)(2-hydroxyphenyl) methanone and 1,3-dihydroxyxanthone. PPA proved to be a more efficient catalyst for the condensation of salicylic acid with phenol, hydroquinone, pyrogallol and catechol while POCl3/ZnCl2 gave higher yields for resorcinol and phloroglucinol. In all cases, ZnCl2 alone did not show significant yield enhancement. The second part of this research work describes a convenient one-pot synthesis of NMethyl-2-pyrrolidone (NMP) an important industrial solvent by a conventional heating process and by microwave irradiation. The intermediate N-Methyl-hydroxybutyramide formed from the exothermic reaction of =-butyrolactone with aqueous monomethylamine, underwent an intramolecular condensation reaction catalyzed by highly active copper powder to form the anticipated product in very good yields.
- Full Text:
- Date Issued: 2011
- Authors: Ndebvu, Rumbidzayi
- Date: 2011
- Subjects: Cyclic compounds -- Synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:18488 , http://hdl.handle.net/11260/d1007382
- Description: The scope of microwave induced synthesis of various cyclic compounds was investigated and considerably expanded. The advantages of this synthetic method were clearly demonstrated when compared to conventional heating methods of organic synthesis. The exposure of organic compounds to continual Ultraviolet (UV) radiation damages the materials and reduces their chemical and physical properties and in most cases irreversibly and this is not only a concern for industry but for consumers as well. Particularly prevalent are incidences of skin cancer now linked to UV radiation. Research efforts are directed towards finding cheap and efficient UV-absorbers to protect such light sensitive materials. Phenyl salicylates and hydroxybenzophenones constitute families of UV-absorber compounds, and this has necessitated this research. The condensation of differently substituted phenols with salicylic acid, catalyzed by either phosphoric acid (PPA), POCl3/ZnCl2 or ZnCl2 afforded the anticipated phenolic type UV -absorber molecules such as phenyl salicylate, 4-hydroxyphenyl-2-hydroxybenzoate, 2,3-dihydroxyphenyl-2-hydroxyphenylbenzoate, 3-hydroxyphenyl-2-hydroxybenzoate, (2,4-dihydroxyphenyl)(2-hydroxyphenyl)methanone, (2,3-dihydroxyphenyl)(2-hydroxyphenyl) methanone and 1,3-dihydroxyxanthone. PPA proved to be a more efficient catalyst for the condensation of salicylic acid with phenol, hydroquinone, pyrogallol and catechol while POCl3/ZnCl2 gave higher yields for resorcinol and phloroglucinol. In all cases, ZnCl2 alone did not show significant yield enhancement. The second part of this research work describes a convenient one-pot synthesis of NMethyl-2-pyrrolidone (NMP) an important industrial solvent by a conventional heating process and by microwave irradiation. The intermediate N-Methyl-hydroxybutyramide formed from the exothermic reaction of =-butyrolactone with aqueous monomethylamine, underwent an intramolecular condensation reaction catalyzed by highly active copper powder to form the anticipated product in very good yields.
- Full Text:
- Date Issued: 2011
Mohair and wool fibre surface structure and lustre determination
- Ndlovu, Ntombizikhona Beaulah
- Authors: Ndlovu, Ntombizikhona Beaulah
- Date: 2011
- Subjects: Mohair and wool fibre -- Lustre
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:18484 , http://hdl.handle.net/11260/d1006641
- Description: Textiles have always been one of the essential materials for people and have a great variety of uses such as in clothing, agriculture, medical, automotive and aerospace applications. The sort of properties needed for any type of fabric basically depend on the structure of the fibre surface. Of many geometric attributes that can be used to describe the surface appearance of a fibre, yarn, or fabric sample, one of the more common is lustre. Mohair and wool fibre surface structure have been studied using optical microscopy and Atomic Force Microscopy (AFM). Optical microscopy was also used to take fibre diameter measurements. Another technique, goniophotometry, was used to make quantitative lustre measurements of mohair and wool fibres. The surface structure of mohair has got a faint pattern of scales where the scales are generally unpronounced or flat and relatively long. Wool has got a scaly surface structure where the scales overlap leading to interlocking of fibres. The scale configuration on the surface of mohair and wool fibres also differs. A qualitative connection between fibre lustre and the fibre surface structure was found. Because of its smooth surface relative to that of wool, mohair reflects a greater amount of incident light specularly whereas wool reflects most of the incident light diffusely. In general, mohair fibres have a higher lustre than wool due to its less prominent cuticle structure found on its surface. Furthermore, mohair fibres with the smallest diameters give an even higher lustre.
- Full Text:
- Date Issued: 2011
- Authors: Ndlovu, Ntombizikhona Beaulah
- Date: 2011
- Subjects: Mohair and wool fibre -- Lustre
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:18484 , http://hdl.handle.net/11260/d1006641
- Description: Textiles have always been one of the essential materials for people and have a great variety of uses such as in clothing, agriculture, medical, automotive and aerospace applications. The sort of properties needed for any type of fabric basically depend on the structure of the fibre surface. Of many geometric attributes that can be used to describe the surface appearance of a fibre, yarn, or fabric sample, one of the more common is lustre. Mohair and wool fibre surface structure have been studied using optical microscopy and Atomic Force Microscopy (AFM). Optical microscopy was also used to take fibre diameter measurements. Another technique, goniophotometry, was used to make quantitative lustre measurements of mohair and wool fibres. The surface structure of mohair has got a faint pattern of scales where the scales are generally unpronounced or flat and relatively long. Wool has got a scaly surface structure where the scales overlap leading to interlocking of fibres. The scale configuration on the surface of mohair and wool fibres also differs. A qualitative connection between fibre lustre and the fibre surface structure was found. Because of its smooth surface relative to that of wool, mohair reflects a greater amount of incident light specularly whereas wool reflects most of the incident light diffusely. In general, mohair fibres have a higher lustre than wool due to its less prominent cuticle structure found on its surface. Furthermore, mohair fibres with the smallest diameters give an even higher lustre.
- Full Text:
- Date Issued: 2011
The value of remnant habitat patches for conserving butterflies (Lepidoptera) in King Sabata Dalindyebo (KSD) Local Municipality, Eastern Cape, South Africa
- Authors: Avuletey, Richard
- Date: 2011
- Subjects: Butterflies -- Research Butterflies -- Behaviour South Africa -- Transkei
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:18490 , http://hdl.handle.net/11260/d1011285
- Description: Butterflies (Lepidoptera) have attracted more attention as indicators of terrestrial ecosystems than other invertebrates. This taxon is widely used as tools or subjects for biodiversity conservation planning in the Northern and Southern Hemispheres. The study determined butterfly species turnover at a-priori selected habitat patches in a protected area (Nduli Nature Reserve) and non-formally protected areas (outside Nduli Nature Reserve) of the KSD Local Municipality and their response to measured environmental variables. Using transect survey methods, 516 butterfly individuals belonging to 22 species were caught from 16 sampling units. Species dominance curves showed more butterfly species evenness outside reserve sites than inside. Hierarchical clustering using Bray-Curtis similarity matrices and Correspondence analysis (CA) grouped sampling units according to butterfly species sampled. Site habitat patches outside the reserve were richer in butterfly and overall abundance than inside the reserve. The Canonical Correspondence analysis (CCA) results revealed that certain site variables such as percentage herb cover, area of patch size, average grass height, grazing intensity, distance to the city centre and average flower density accounted for species distribution patterns at various sampling units. The conservation implications of the study suggest that patch level management of micro-habitats with sufficient flowering herbs, structural vegetation, and patch size with minimal disturbance within and outside reserve areas can encourage rare and common butterfly species richness and diversity.
- Full Text:
- Date Issued: 2011
- Authors: Avuletey, Richard
- Date: 2011
- Subjects: Butterflies -- Research Butterflies -- Behaviour South Africa -- Transkei
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:18490 , http://hdl.handle.net/11260/d1011285
- Description: Butterflies (Lepidoptera) have attracted more attention as indicators of terrestrial ecosystems than other invertebrates. This taxon is widely used as tools or subjects for biodiversity conservation planning in the Northern and Southern Hemispheres. The study determined butterfly species turnover at a-priori selected habitat patches in a protected area (Nduli Nature Reserve) and non-formally protected areas (outside Nduli Nature Reserve) of the KSD Local Municipality and their response to measured environmental variables. Using transect survey methods, 516 butterfly individuals belonging to 22 species were caught from 16 sampling units. Species dominance curves showed more butterfly species evenness outside reserve sites than inside. Hierarchical clustering using Bray-Curtis similarity matrices and Correspondence analysis (CA) grouped sampling units according to butterfly species sampled. Site habitat patches outside the reserve were richer in butterfly and overall abundance than inside the reserve. The Canonical Correspondence analysis (CCA) results revealed that certain site variables such as percentage herb cover, area of patch size, average grass height, grazing intensity, distance to the city centre and average flower density accounted for species distribution patterns at various sampling units. The conservation implications of the study suggest that patch level management of micro-habitats with sufficient flowering herbs, structural vegetation, and patch size with minimal disturbance within and outside reserve areas can encourage rare and common butterfly species richness and diversity.
- Full Text:
- Date Issued: 2011
- «
- ‹
- 1
- ›
- »