Change search
Refine search result
1 - 12 of 12
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Chidambaram, R
    et al.
    Karobio.
    Garg, N
    Karobio.
    Rasmuson, Åke Christoffer
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Gracin, Sandra
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Improved crystalline material2006Patent (Other (popular science, discussion, etc.))
  • 2.
    Gracin, Sandra
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Polymorphism and Crystallization of p-Aminobenzoic Acid2004Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    Polymorphs are solid phases where the chemical composition isequal but the crystal structure differs. Many organic compoundsmay appear in more than one crystalline structure. The differentpolymorphs of a givensubstance may have significantly differentphysical properties (packing, thermodynamic, spectroscopic,kinetic, surface and mechanical properties). Sometimes the moststable polymorph is difficult to produce or a metastable form hasfavourable properties.

    This thesis focuses on the crystallization of p-aminobenzoicacid. This model compound crystallizes in two differentpolymorphic forms:

    1) the α-polymorph, which isthe commercially available form and appears as long, fibrousneedles 2) the&#946-polymorph, that appears in the form ofprisms.

    The thermodynamic stability and crystallization from differentsolvents have been studied experimentally. The system is found tobe enantiotropic with a transition temperature of 25 °C,below which theβ-form is the stable polymorph. The compoundhas been crystallized from thirteen different solvents, either byslow cooling after which the product is allowed to mature insuspension, or by rapid cooling followed by immediate isolation.Needles were obtained from all solvents by both methods. In waterand ethyl acetate below 20°C the prismaticβ-form isobtained however, often together with the needles. Theβ-formcrystals usually needed hours or days to grow at the very slowcooling used, while needles usually appeared in seconds. Bycareful control of supersaturation and temperature coolingcrystallization can be performed to produce the pure β-formin water and in ethyl acetate. The influence of the solvent isexplained by analysis of the crystal structures versus thepossible interaction of the solvent molecules with the solute insolution. The α-form structure is governed by dimers and iskinetically favoured because the dimers easily form in thesolution especially in less polar solvents. The crystal structureof the β-modification is not based on dimers but on fourmembered rings with alternating amino and carboxyl groups.

    Keywords:controlled crystallization, polymorphism,p-aminobenzoic acid

  • 3.
    Gracin, Sandra
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Solubility and polymorphism of molecular compounds2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis deals with the controlled crystallization of small organic molecules and is focused on solubility and polymorphism. The solubility was determined for phenylacetic acid, p-hydroxyphenylacetic acid, p-aminophenylacetic acid, p-hydroxybenzoic acid and ibuprofen in both water and in a range of organic solvents. Data is discussed from the standpoint of molecular aspects of solute – solvent interactions and by estimated solid phase activity. It was shown that better understanding could be acquired by making a qualitative analysis of the molecular interactions in the solution and the crystal structure of the compounds in question.

    Solubility predictions that are carried out by the UNIFAC method are not sufficiently accurate to serve as a basis for a reliable design of a crystallization process or selection of a suitable solvent since they deviate more than 15% from experimental values. The reason for the discrepancies are related to uncertainties in the prediction of activity coefficients by UNIFAC, as well as, difficulties in the estimation of the activity of the solid state.

    p-Aminobenzoic acid (PABA) has been crystallized from thirteen different solvents either by slow cooling, after which the product is allowed to mature in suspension, or by rapid cooling followed by immediate isolation. Two different polymorphs have been crystallized. The system is found to be enantiotropic with the transition temperature of 25 °C, below which the β-form is the stable polymorph. The α-form was obtained from all solvents by both methods. The β-form is obtained only in carefully controlled conditions from water and ethyl acetate, well below the transition temperature. Often the α-form appears concomitantly.

    It is shown in this work that sonication significantly reduces the induction time for nucleation. The β-form crystallizes more reproducibly and at higher cooling rates when controlled sonication is used. In addition sonication is found to selectively favor the appearance of one of the polymorphs. Producing the pure β-form was possible even above the transition temperature where other crystallization techniques were only capable of producing the stable α-form. The α-form structure is based on centro symmetric dimers formed by association of carboxylic acid groups. It is suggested that the preference for nucleation of the α-polymorph is related to the formation of dimers in the supersaturated solution. Only at the condition where the formation of dimers is reduced sufficiently, (i.e. in the polar solvents or when sonication is applied) the nucleation of the β-form is favored.

  • 4.
    Gracin, Sandra
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Prediction of Solubility of Solid Organic Compounds in Solvents by UNIFAC2002In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 41, no 20, p. 5114-5124Article in journal (Refereed)
    Abstract [en]

    Predictions of solubility of nine different solid organic fine chemical compounds in water and organic solvents of relevance to industrial processing are examined. UNIFAC interaction parameters are taken from standard reference literature, extracted from liquid-vapor equilibria. For most systems, predicted solubilities deviate more than 15% from experimental values. Deviations are due to uncertainties in the estimation of the activity of the pure solid as well as to deficiencies in the estimation of activity coefficients in the solution. By comparison with results from ab initio quantum chemical calculations of the elecrostatic potential on the molecular surface of the solutes, it can be shown that a key assumption of the UNIFAC approach is not necessarily fulfilled. The properties of a functional group may depend significantly on the properties of the rest of the molecule.

  • 5.
    Gracin, Sandra
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    4-Hydroxyphenylacetic acid2005In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. 61, no 6, p. O1919-O1920Article in journal (Refereed)
    Abstract [en]

    The crystal structure of commercially available 4-hydroxyphenylacetic acid, C8H8O3, is non-centrosymmetric, with four hydrogen bonds between each molecule and adjacent molecules. The hydrogen bonds link the molecules in the crystal structure into an infinite three-dimensional framework.

  • 6.
    Gracin, Sandra
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Redetermination of the beta-polymorph of p-aminobenzoic acid2005In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. 61, no 5, p. O1242-O1244Article in journal (Refereed)
    Abstract [en]

    Single crystals of p-aminobenzoic acid, C7H7NO2, were grown from water. In the structure, there is one molecule of the acid present in the asymmetric unit. Hydrogen bonds between adjacent molecules lead to the formation of a three-dimensional network.

  • 7.
    Gracin, Sandra
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Polymorphism and Crystallization of p-Aminobenzoic Acid2004In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 4, no 5, p. 1013-1023Article in journal (Refereed)
    Abstract [en]

    p-Aminobenzoic acid (PABA) crystallizes in two different polymorphic forms: the alpha-polymorph, which is the commercially available form and appears as long, fibrous needles, and the beta-polymorph, which appears in the form of prisms. The thermodynamic stability and crystallization from different solvents have been studied experimentally. The system is found to be enantiotropic with a transition temperature of 25degreesC, below which the beta-form is the stable polymorph. The compound has been crystallized from 13 different solvents, either by slow cooling after which the product is allowed to mature in suspension, or by rapid cooling followed by immediate isolation. Needles were obtained from all solvents by both methods. In water and in ethyl acetate, at slow cooling below 20degreesC, the prismatic beta-form is obtained, however, often together with the needles. The beta-form crystals usually needed hours or days to grow at the very slow cooling used, while needles usually appeared in seconds. By careful control of supersaturation and temperature, cooling crystallization can be performed to produce the pure beta-form in water and in ethyl acetate. The influence of the solvent is explained by analysis of the crystal structures versus the possible interaction of the solvent molecules with the solute in solution. The alpha-form structure is governed by carboxylic acid dimers and is kinetically favored since it is believed that the corresponding dimers easily form in the solution, especially in less polar solvents.

  • 8.
    Gracin, Sandra
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Solubility of Phenylacetic Acid, p-Hydroxyphenylacetic Acid, p-Aminophenylacetic Acid, p-Hydroxybenzoic Acid, and Ibuprofen in Pure Solvents2002In: Journal of Chemical and Engineering Data, ISSN 0021-9568, E-ISSN 1520-5134, Vol. 47, no 6, p. 1379-1383Article in journal (Refereed)
    Abstract [en]

    The solubility of phenyl acetic acid, p-hydroxyphenylacetic acid, p-aminophenylacetic acid, p-hydroxybenzoic acid, and ibuprofen in water and in a range of organic solvents of relevance to industrial processing is reported. The solvents used are water, methanol, ethanol, 2-propanol, acetone, 4-methyl-2-pentanone, ethyl acetate, chloroform, and toluene. Solubility data are discussed from the standpoint of molecular aspects of solute-solvent interactions and by estimated solid-phase activity.

  • 9.
    Gracin, Sandra
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Svärd, Michael
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
    4-aminophenylacetic acid2005In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. 61, no 6, p. O1536-O1537Article in journal (Refereed)
    Abstract [en]

    Crystals of the title compound, C8H9NO2, were obtained from ethyl acetate. The structure consists of the acid in its zwitterionic form. In the crystal structure, each molecule interacts through strong N-H center dot center dot center dot O hydrogen bonds with six adjacent molecules, yielding a three-dimensional network.

  • 10.
    Gracin, Sandra
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Uusi-Penttilä, Marketta
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Influence of ultrasound on the nucleation of polymorphs of p-aminobenzoic acid2005In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 5, no 5, p. 1787-1794Article in journal (Refereed)
    Abstract [en]

    p-Aminobenzoic acid crystallizes in two different polymorphic forms: the alpha-form and the beta-form. The alpha-form crystals are needle-shaped, while the beta-form crystals have a more favorable prismatic shape. The system is enantiotropic with the transition temperature at approximately 25 degrees C. Below the transition temperature, the beta-form is the thermodynamically stable polymorph but can only be produced at very slow supersaturation generation either in water or in ethyl acetate. In the present work, the influence of ultrasound on the nucleation of p-aminobenzoic acid polymorphs has been investigated by use of several different sonication intensities and schemes. It is shown that sonication significantly reduces the induction time for nucleation. By using controlled sonication, we were able to more reproducibly crystallize the beta-form at more reasonable cooling rates. In addition, sonication is found to quite selectively favor the appearance of the beta-polymorph. It is even possible to produce the pure beta-form above the transition temperature where it is the metastable form and impossible to produce without sonication. The alpha-form structure is based on centro symmetric dimers formed by the association of carboxylic acid groups, while the beta-form contains four-membered hydrogen-bonded rings of alternating amino and carboxylic acid groups. It is suggested that ultrasound disturbs the building up of the dimers in the solution and thus favors the crystallization of the beta-polymorph.

  • 11.
    Gracin, Sandra
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Uusi-Penttilä, Marketta
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Rasmuson, Åke Christoffer
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Controlling polymorphism of p-aminobenzoic acid by sonication2005In: the 16th International Symposium on Industrial Crystallization, VDI verlag Dusseldorf , 2005, p. 677-682Conference paper (Refereed)
    Abstract [en]

    The influence of ultrasound on the nucleation of p-aminobenzoic acid in supersaturated aqueous solutions has been investigated. The induction time and the solid phase structure has been determined in experiments with and without ultrasound. Different sonication schemes and intensities have been evaluated. It is found that sonication leads to a much shorter and reproducible induction time. In addition, it has been found that sonication preferentially favor the formation of one of the polymorphs.

  • 12.
    Svärd, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Gracin, Sandra
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Oiling out or molten hydrate-liquid-liquid phase separation in the system vanillin-water2007In: Journal of Pharmaceutical Sciences, ISSN 0022-3549, E-ISSN 1520-6017, Vol. 96, no 9, p. 2390-2398Article in journal (Refereed)
    Abstract [en]

    Vanillin crystals in a saturated aqueous solution disappear and a second liquid phase emerges when the temperature is raised above 51 degrees C. The phenomenon has been investigated with crystallization and equilibration experiments, using DSC, TGA, XRD and hot-stage microscopy for analysis. The new liquid solidifies on cooling, appears to melt at 51 degrees C, and has a composition corresponding to a dihydrate. However, no solid hydrate can be detected by XRD, and it is shown that the true explanation is that a liquid-liquid phase separation occurs above 51 degrees C where the vanillin-rich phase has a composition close to a dihydrate. To our knowledge, liquid-liquid phase separation has not previously been reported for the system vanillin-water, even though thousands of tonnes of vanillin are produced globally every year.

1 - 12 of 12
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf