@JsonConvert.SerializeObject(new Dictionary<string, string>
{
    { "@context", "http://schema.org" },
    { "@type", "Organization" },
    { "name", "HAHA" },
    { "url", "http://example.com" },
    { "logo", "http://example.com/image.png" }
})

{"@context":"http://schema.org","@type":"Organization","name":"HAHA","url":"http://example.com","logo":"http://example.com/image.png"}